Option 1 : Import F 35
Lets say India negotiates (begs) US to allow purchase of 36 F 35 aircraft throughout 2025-26. Finally US agrees and in 2026-27 a deal is signed for ~$8 bn.
The deal will include US weapons like AIM 120 C7, JDAM, etc and WILL be subject to US rules and regulations regarding intended usage. Also, India will have ZERO access to IP and will need to reply on US contractors to service these aircraft.
The first aircraft will be delivered 4-6 years after the signing of the deal (2030-2031). Then the rest over the next two years (2032-2033).
Option 2 : Persist on AMCA
By comparison, AMCA rollout is scheduled for 2026, which is reasonable given titanium bulkhead cutting and other small scale part manufacturing started in 2022.
First flight, depending on how many subsystems are installed in the AMCA will be 2027-2028. Then add another 3 years of tests (weapon-radar integration, certification, flight envelope tests, manuals, troubleshooting, compatibility) and by 2030-31 you have a somewhat ready IOC capable fighter.
Another 2 years 2032-2033 you have a FOC capable AMCA. If we sign GE F414 engine deal in 2025 (hopefully) and it takes 2 years to build the facility while we import some GE F414 engines as part of the deal, then by 2027 facility is ready. By 2028 domestic assembly of GE F414 commences and by 2031-32 everything is in place for AMCA to be mass produced and inducted.
Conclusion :
In both cases, India won't receive a 5th generation fighter before 2031-32 at the earliest. Bear in mind that it will take another 2-3 years to have at least 2-3 operationally ready squadrons of the F 35/AMCA so ~2034.
India needs to produce more SU 30 MKI, mass produce Tejas MK2, finish the 180 Tejas MK1A and missile-radar max until the mid 2030s.