Started a new kingdom.
Discovered pact maker at level 1, got scholar's pact
didon't have enough piety for it to trigger
found mysteria at level 5, leveled up to level six (had 44 piety)
Scoolar's pact charged for almost all my piety (40)
when I leveled up to level 7, i had 26 piety, leveled up, it charged me for 20 piety
Leveled up to level 8, had 24, piety, scholar's pact charged me for 20 piety
this seems to apply to all pacts, and can sometimes lead to god punishment (GG punished me for converting an item, thanks Spirit pact)