Best arrangement for working hours

I currently work 5 evenings a week in an admin role. Thankfully, my employer is generally very flexible with hours, working patterns and remote working. This means I should be able to adjust my days/hours to fit around my studies.
My question is, what sort of arrangement should I ask my employer for? Are there particular weekdays I should try and keep clear (if societies/lectures tend to be held on certain days)?
My initial thoughts are to ask for a reduction to 3 days (evening shifts). However, if most stuff is on in the day/weekend, it seems a shame to lose several hundred pounds a month unnecessarily! Would appreciate any thoughts/insight from past, present or prospective students?
It’s worth mentioning that I will be 26 when starting the course.