If a challenge for certamen is issued, can the one challenged hold out for a time or place of choice?
For example: Special circumstances in caves (or at dawn), Merenita wanting it to be moved to nearby faerie aura, Challenge occurs in dominion aura and challengee wants to move it to nearby magic aura.
Maybe, but not by the Code, only if they can negotiate it on their own.
The considerations are that it must be "mutually acceptable" - but otoh, begging off for advantage (or to lose a disadvantage) may be viewed poorly.
Afaik, nothing that forces the challenger to accept a delay or change of venue - "here and now" is as good as "mainstreet, high noon", "at dawn on the glen", or "first lightning storm we get, top of the highest tower".
That is why I asked. The code demands you accept and customs for technique and form but most code duello has provisions for determining the time and place.
Does the code require "Here and Now" from the one challenged?
By the way, the reason that this came up, I was thinking about a certamen in a game. I realized that if my maga had been part of that certamen, it would have been over very very fast since the opponent would have gotten -9 for aura while she got +6 for aura.
It does raise some interesting considerations re strategies. If you know/suspect someone has Cyclic Magic or other situational/environmental modifiers, do you wait until they are at their low? Can they demand that you wait until they are at their high? How long is reasonable to wait?
{shrugs}
Probably, certamen should be resolved quickly.
A challenge for a duel in two months in Cairo is really mean: It makes your opponent lose a season or two in traveling (unless Re is high enough to teleport). But saying no doesn't seem to be an option in a certamen that isn't for love.
Yeah, that's what it was designed to do, AFAIK, to quickly and "amicably" resolve conflicts without having to wait until the next Tribunal.
That and as a club for Tremere. 
How does the Aegis affect Certamen? Assume one participant is visitng and doesn't have a token.
TO the question of aegis VS Certamen, I would say that the Aegis does affect all rolls of Certamen. However, politically, insisting on a "right here" Certamen when the challenged party responded "I take the challenge, but let's step out first"... would probably be frowned upon. In tribunal I would vote in favor of the guy who insisted to have the certamen outside.
That opinion applies to Aegis of the Hearth as a generic, universal condition. If a wizard has a funny realm allegiance, or a cyclic magic, or an environmental bonus/penalty, then I would say that's part of the game, much like abiding by the opponent'schoice of Art is also part of the game.
Agreed in principal, but what if the challengee had a Restriction, one that prevented all magic in whatever environment was "here and now"? Is it game over?
Most restrictions are something that one can evade with some small effort, but not all - some involve more abstract states of existence, things that cannot be changed by "stepping outside" or even after a couple minutes of prep.
In that case, on the one hand, I'd agree - that's the game, that's the life of a mage, bad luck old bean! But, on the other, IC or OOC it would not be satisfactory to see a mage constantly abused once their Restriction was known, either by one challenger or the Order as a whole.
("Certamen against Bob? Hey, just make sure there's a thunderstorm going - he's useless!"
And so they line up...)
I had never thought about Aura and Certamen until it came up in the game Lady Phoenix is referring to. In fact, I probably still wouldn't have paid attention to it except for the fact that one of the duelists rolled a "0", and I realized he should roll additional botch dice for the Divine aura. The two were on even ground, both being regular magi equally affected by the Divine. But it does bring up all kinds of ideas for situations: a Merinita dueling in a Faerie aura, the Holy Maga in a Divine Aura, the Infernal magus, and so on.
Here's a question that came up a while back... can you wait/stall until your apprentice can go to your room and fetch the vis?
I could easily see a delay for a short time to a better location (within reason, such as out of town when in public inn, private room if in tribunal, until morning.).
The question is what is the traditions of a code duello to apply since that is what certamen is. I could easily see delays up to 24 hours and change of locations up to distance from center of city to outskirts. The more private the current the location the less a location change is appropriate (for example in a covenant, just until you are outside the aegis)
That all makes sense to me - certamen is the gentleman's answer to a dispute before invoking the Code and a Tribunal, after all. If word gets around that a magus is deliberately making use of opponent's weaknesses in certamen to engineer political advantage then he's going to develop a black, if somewhat admiring in certain circles, reputation and possibly find decisions going against him at Tribunal. A magus known for being fair about it, on the other hand, is more likely to find that people are willing to trade book copies and vote in his favour.
I suspect that far more than just saga dependent, this is heavily tribunal and covenant dependent as well with some favouring immediate resolution and others requiring witnesses and a formal event. I can see having either a Flambeau or a Tytalus trying to get a code duello formalised at Tribunal would make for a great story hook, and shake the Tremere cage quite enthusiastically.
It is impact of Aegis on casting/magic that makes slight changes reasonable. THat and considering effect of CrIg certamen in middle of a wooden inn?
I'd argue the other way. Certamen is a proxy for war: the more the code duello pulls it away from a real proxy for war, the -less- significant it is. It becomes a sport, like fencing. So I think using an opponent's weaknesses against him are fine, because you'd do that in a war. Fairness doesn't come into it, except insofar as things which make a person who would lose a war win at Certamen are likely unfair.
The resolution of a certamen needs to be seen as "fair" by both parts to really hold. If you feel you were beaten because you were unduly handicapped nothing prevents you from declaring WW, so the certamen becomes meaningless as a non lethal resolution method. It needs to be "fair" and acceptable somehow, even if the ability of both contenders is grossly unequal
I think certamen sucks to start with as a way of resolving disputes, but given the setting, I would think it is like a "duel at dawn" scenario more than a "kick him in the croch since he is drunk now and unable to retailate" kind of approach.
I like the duel at damn approach image as well, since it leaves the opponent senseless for most of the day 
"Dead" for a couple hours
Xavi
Maybe, but if there is a restriction in play and it can be resolved by slight move of location or short wait, it makes sense to allow such because otherwise all you do is create automatic defeat which will basically be followed by wizard war, destroying the purpose of Certamen to negate wizard wars.
Considering the purpose is to avoid wizard war, there needs to be perhaps some ability to adjust time and place (of course change of time followed by not showing up is a loss as admitting defeat). COnsidering wizard war requires a full month notice before it can begin. up to a day in time and location for moving out of AEgis or away from mundanes is reasonable provided there is not extenuating circumstances.
If certamen is about something that is going to happen immediately and a delay means loss (certamen for leadership of expedition about to leave in 2 hours, can't be delayed until next day), then delay is not allowed.