why men have to cut hair and when we should not cut and why not during chathurmas period

 this info is very clearly given in the bellow link.

this doc explains about the reasons and linked it with raja thama gunas entering our body though open cut hairs. 

he also mansions why we should not cut hair in the night and during festivals and on birthday

https://www.hindujagruti.org/hinduism/cut-hair