Hi,
Summing up my thinking on this:
Intended use of Ring: Absolutely not. This requires a virtue such as Amulet from RoPD. I'd certainly allow a Ring to be drawn on the deck of a ship, and probably even on a wall.
Seven Heartbeat Duration: It does go against the usual kinds of duration for Hermetic Magic. OTOH, non-standard durations seem to be explicitly allowed for formulaic spells. OTTH, the actual rules subsequent to the original core rule never include a Formulaic spell with a tweaked duration, unless some Virtue or Breakthrough is involved. This is a remarkable consistency, since spells in published material sometimes have inconsistency with each other, common sense, the core rules and sometimes even Hermetic Limits, to the point that I recommend considering any published spell outside of the core rules to be considered a house rule rather than something to be taken for granted as working.
Is there even a Formulaic in the core rules that has a non-standard duration (and is not marked as a spell that doesn't quite conform to Hermetic standards but is a Founder spell or something like that)? I can't think of one. Treading the Ashen Path does not fall into this category: It does something fancy, ie effectively recast a Mom spell repeatedly for its duration, but the durations remain totally standard. It also folds in nicely to the general effect, changing the area in a way that is aesthetically interesting but not more powerful, unlike this which is purely an arbitrary gimme.
So maybe this rule should be treated as rescinded, because it effectively has been: Hermetic Magic needs a virtue to have a non-standard duration. Or a Breakthrough.
How severely does this duration deviate from the norm? Hermetic durations are all based on astronomical configurations, except for Mom, Conc and possibly Diam (which is based on time, albeit a time based on the sun). None of them are based on a magus' body. (Oh, and I suppose we need to specify just whose heartbeat. Presumably the caster's. But what if the caster dies? What if he has SFB or some other weirdness like a literal heart of stone, and his heart doesn't beat?)
So this duration is pretty far outside the usual too. It is further out there than Ring+Conc or +Conc, which would let a magus concentrate on a spell as it starts to fade, to keep it going as long as he concentrates. It is further out there than Ring+Mom. It's something akin to Ring+2Mom, which is pretty radical.
These aren't non-standard durations that gets +1 because it's a little fancy, but are also strictly and vastly better.
Because once I allow Ring+7hb, why not also allow "Ring + until I urinate 7 times?" Or even Duration of Urination considered as a +2?
Not to piss on this parade.
OTOH, it seems like it would be interesting for a magus to try to create durations that are based on his own body. I can see some Criamon interested in this, or magi influenced by other sources of "body as microcosm reflecting universe."
Anyway,
Ken