How long should battery minder take, in conditioning mode?

Naio, disconnecting AGM makes sense - IMO - because you don't gain anything by keeping it floating. Float charge is necessary to prevent self-discharge in wet batteries, but AGM don't discharge much. Since nobody knows exactly what is going on inside that sealed black box, this is just my 2 cents.

I keep my AGM floating (and automatic daily 14.6V for a few seconds) because they've developed a huge self-discharge after a year. Must be a lemon from China.