reverse communion slave orders

[aaminoff]

I have been meaning to ask about this, in the context of Blood Sabbaths.

So if you are a B1 mage, Sabbath Slave costs 100 fatigue. Sabbath Master costs 100 fatigue likewise. So that implies that if you do

slave - S slave
...
master - Sabbath master

and they are all B1 mages, everyone will end the turn asleep at 100+casting fatigue?

Well, thats no good. How about if I forge a communion master matrix, give it to the last guy.

slave
...
master - reinvigorate

The master, already being in the communion, will thus flush everyones' fatigue.

Alternatively, if I have (or can empower/boost) a mage at the beginning of the list to B2, then:

master B2 - S. Master, reinvig
slave B1 - S. slave, do something cool

I guess this would only be useful for a reverse communion where the slaves don't want to cast spells on turn 2, or can hold for a turn before running off.

My question is basically, are we certain that spells take effect at the instant they are cast? There isn't some sort of post-casting fatigue reconciliation phase and the effect of reinvig does not happen till then?