IMPS request being limited with the money limit can be sent on any day. It can be sent on sunday or any other working and non-working day. This service being electronic, does not restricts itself on business days. There are also no national holiday limitations for this service.
Each bank has different policies for IMPS and restriction. You're however restricted to 50,000 per day under IMPS. Do note that depending on your account type the request could be limited even for lower amount. For example some banks have restricted IMPS upto 25,000/- for accounts with zero balance. If you're restricted for IMPS service then it could be due to bank policies and not because of IMPS service itself.