Yup, a 5 hour layover is fine in most cases. As for immigration, I suppose it depends on the airport and when your flight arrives (and what other flights arrive at that time). I don't recall having an issue in DEL or BLR or BOM, and I've even taken those EWR-DEL and EWR-BOM flights.

The OP should also look at options routing through BOM instead of DEL. But economy seating on those 15+ hour flights is torture (to me). I don't know how people stuck in middle-seats do these flights. For anything over 12 hours or so, I look for routes that allow me to get off and stretch my legs. In this case, I'd look for routes via FRA/ZRH/MUC/LHR or somewhere in Asia (TYO, ICN, etc.). Or consider a PE ticket if the price differential isn't that great.