I think of regular tribunals as mostly dealing with "felonies", charges that are punished by fines or, at most, light punishments (equivalent to a few months in prison, perhaps). These are the kinds of "crimes" that can suffer delayed repercussions. Most of the time. Remember that in the real world trials take years too; sometimes even 7 years. Even trials that send people to jail, and - for minor crimes, unless there is a significant flight risk - the accused are not kept in custody until they are found innocent or guilty.
For more serious or immediate cases, the Quaesitors use an assortment of methods. In cases where restitution can be made, such as theft, they lean on the accused to accept a "plea bargain", and on the accuser to accept it too, and present a "done deal" in tribunal. I think Trianoma magi do a lot of such haggling, bringing peace to the Order.
In cases requiring a Wizard's March, one way is to conduct an Emergency Tribunal. I reckon a posse of hoplites, the tribunal's quaesitors, the Praeco, and a few archmagi or other notables could Hermes Portal at a moment notice; not all the people will always show up (depending on what they're currently doing), but it should be possible to convene a quorum quite rapidly, and set out Marching on the spot. It is a rare case where a March is declared in regular tribunal; most often, this is done by imprisoning/chaining the offending magus by a senior Hoplite or Quaesitor in lieu of such an ad-hoc March, which in some tribunals would be standard practice (Thebes) and in others (Stonehenge) unheard of.
When all else fails, the Quaesitor can act on his own or with a self-recruited Hoplite posse, and hope the tribunal will affirm his actions after the fact. It almost invariably will, except in tribunals where the Quaesitors, or this particular one, are in poor standing (Rhine). Just like police officers almost always aren't accused of murder when they shoot someone down, and tend to get only a "slap on the wrist" for errors of judgment that result in offences that would send citizens to jail (there are exceptions, of course).
All that said, there is always room for nefarious magi to operate "below the radar" of Quaesitors and the Order, but I actually would pull some Divination shticks to forestall any serious scheme from proceeding far without Quaesitors coming to sniff around. There are plenty of ways to divine the future in canon (although I'm critical of the mechanics of some...), and there is no reason House Guernicus won't employ some to look after the Code, Order, and Tribunal (in this order...).
Cheers,
Yair