Good questions for post-class survey
I've always used the following in ALL of the classes I teach:


What did you like most about quantitative basket weaving? [free text]
What would you most like to see changed for quantitative basket weaving? [free text]
How valuable do you feel your time has been in quantitative basket weaving? [1-10]
Do you have any other comments about the module?


To these I will often add 3-5 other questions which I'm curious about. Sometimes it is to test the waters on new things I'm planning on trying with them or future classes.

The key is to keep it short. ~5 minutes is way too long. If you take more than 1-2 minutes of students' time, you are very unlikely to get many responses.

I usually ask these questions at mid-point and after the final class. However, if you want more frequent feedback, I'd suggest the "one minute paper" where you ask two simple questions (paper, electronically, whatever fits):


What do you think is the most important thing you learned today (or this week)?
What did you find the most difficult point to understand?


One minute papers are useful for constant course corrections while the earlier questions are more to find out how to change the design of the module next time (or next half).