TIMATIC specifically states TWOV cannot be done on separate tickets:
TWOV (Transit Without Visa)
Passengers transiting through Bangalore (BLR), Chennai (MAA), Delhi
(DEL), Kolkata (CCU) or Mumbai (BOM) with a confirmed onward ticket
for a flight to a third country within 24 hours. The connecting flight
must be booked on the same ticket and the luggage must be checked to
the final destination.
They must stay in the international transit area of the airport and
have documents required for the next destination.
It's something I looked into in the past as well, it was easier just to get the visa.