Hey Salim,
72 hours is typically how we do the refresh. a 50/50 media change, with the drug + media formulation going in at 2x concentration (so post dilution you have your 1x concentration).
For some stuff (e.g. antibody treatments) we have done a refresh at 48 hours, but typically 72 hours is what we do!
Good luck and hope you have a good break/Christmas/New year! As ever, thanks for TOOTING ;)
Abs