The wording of the Wizard's Communion effect is
"One magus must roll for success as if casting the specified spell himself. However, the target number for the spellcasting roll is the spell's level divided by the number of magi participating in the Communion."
Because Wizard's Communion is meant to apply to Formulaic spells, where casting time isn't really factored, this topic doesn't really come up; but in the case of casting a ritual spell using Wizard's Vigil, where time is a factor, how long does it actually take to cast the ritual?
The passage carries on with,
"So if five magi participate to cast a 50th level spell, the caster would have to successfully cast a 10th level spell."
Considering that the Communion effect grants every other benefit of casting a spell as-if it were a lower level than it actually is-- higher penetration, easier totals --I would tend to assume that this means a ritual is also cast more quickly, since that would also be an innate consequence of a lowered level; in this case, taking the casting time down from two and a half hours to thirty minutes.
Is that a correct reading or would the ritual take the same amount of time because you're still performing a ritual of that magnitude? None of the wording in Communion suggests that the spell being cast is fundamentally changed-- in fact, the opposite --the spell is still 50th level, it's just being cast as-if it were 10th level.
Help would be appreciated