I've seen versions of this question asked but nothing exactly corresponding to my situation.

I am arriving inbound on UA 48 to BOM at around 9PM, and leaving at 5:15 the next morning on an Air India flight to Goa. Air India to Goa departs from the international terminal.

I am curious about the prospects for staying overnight at the airport (I've currently booked the Hyatt Regency on points but I'd save them if I thought I could do so easily). Will I be able to stay in the terminal / would I be able to access one of the clipper lounges, or will I have to wait until 3 hours before my flight because I'm transferring international to domestic even though in the same physical terminal building?

If I left the airport to go get a late dinner and then came back, would I be able to enter at midnight? Would I be able to access a lounge at that time? Are the lounges available 24 hours?