Zoemi really did check everything out – not only did he extensively question the students who trained with him about the sneaking out at night part - he even made sure that none of the capture targets have any plans that would lead them to that pond during midnight, and, first and foremost, he learned from teacher Kros that the heroine would be helping him out with his health issues, so she would be not only in the completely different part of the Academy but she would also be under the supervision of the teacher the entire time, leaving her no chance to sneak out!
It was perfect – this time the scarred attendant didn't leave anything up to chance and made sure that nothing would disturb his master's date!
The little thing about sneaking out – he learned to form his training buddies.
Same with the schedules and plans of the other capture targets, as he wasn't training with first years but with a few second-year students too.