It doesn't actually make any sense for summoning spells to work, but calling spells (like Gate) not to. The only summoning spells, the Summon Monster line, have ridiculously short durations, as I pointed out before. Redcloak would have to have known down to the minute when his targets would arrive for his demons to actually still be around when they showed up, because even if he could extend the spell (and for Summon Monster 9 he couldn't) it would barely last more than 3 minutes. The only summoning-style spells with longer durations are calling spells - the Planar Ally line, the Planar Binding line, and Gate.
Zevox