Tactics for Conflux.

The duration depends on the amount of magic power, 10 power = 10 rounds. Also, cast healing spells on your units if they are slowed. In my opinion, 3 schools of magic might be too much.

The guy was asking about something slightly different. The idea is that mass haste and mass slow will be more preferable to cast, so mass bless can be postponed for a few rounds.
Regarding the topic - that's true, so it's better to level up 2 schools of magic, and the third one closer to the end of the hero's development, if needed. Water is generally good for Conflux, I usually take it if there's a bless spell available.