May I ask professors to reschedule two back to back night classes from 4:30PM to 9:00PM?

Academic timetabling is a notoriously difficult problem. Professors have several classes to teach, students have several classes to attend. There are restrictions related to classroom sizes, specific equipment (e.g. computer labs). Some professors may have individual restrictions, e.g. can only teach on specific days or hours due to other commitments.

Normally, Professors do not decide their own timetables, but submit their preferences to the Timetabling Office, which then generates a timetable for everyone. Students can also try to submit their requests, but usually as a groups (cohorts), not individually. If you are not happy with your timetable, it is definitely worth trying to change it, but bear in mind that it may not be easy.

However, if you class is scheduled up until 9pm, which is significantly beyond the core hours, you actually have a much better chance of having this class rescheduled, particularly if any of other students attending the same late class have caring responsibilities. Your Student Rep / Student Union Rep / Athena Swan Rep (in the UK) might be able to help you with the process.

Yes, you can ask. However, it is likely that professors cannot change the schedule. It is also quite possible that it is too late for anyone to change the schedule. It depends on individual circumstances.

It would be normal for a three hour class to contain a rest break. This may solve your problem.

4:30 pm is an odd time for an evening class to start; chances are that it was selected either specifically to fit into the professor's schedule, or specifically to allow motivated students to attend both the 4:30 class and a 6 pm class.

(For example, some students may find it far more convenient to travel to campus one day a week for a 6 hour session than to travel on two different days.)

In addition to asking if the classes can be rescheduled for your convenience, you might also ask if there other classes you can take towards your degree.