He'll want this one. With a similar spell bonus from Patient Spell his lab total is 68 he'll take a nocturnal lab schedule for a season to get his lab total to 70 and learn it at level 35
If patient spell doesn't apply, then his Rego Vim total is 64 so he can get a level 32 spell in a season. He'd take diurnal watching ward from earlier in the thread at level 30 so he can still load up level 40 spells in it (and take an extra four days for R&R because he can use the lower lab total).
I'm thinking that this is the same effect at a different duration but there is a triggering aspect to Watching Ward that Patient spell doesn't have. Is this enough of a change to make the effect closely related rather than the same?
While I think that this spell follows the guidelines as intended, if it were my game I might invoke the central rule and make it a bit more difficult to pull off. It seems too easy to collect a few hundred trapped spells to go all off at a specified moment for me to be comfortable with the balance of it.