As for AMCA, India should have a pretty good idea of what is available from the majors by now. If a decision were made to go ahead today, I think it extremely likely that a certified engine for AMCA could be available early 2030's. I say 'could be available' because how much Indian 'bureaucracy' would slow project progress down is difficult to anticipate. I have heard nothing to make me think that the culture of glacially slow decision making, so loved in Indian procurement, is changing.
I think 2040 for a new AMCA engine is more credible than 2035. Or never if India is not prepared to bite the bullet and agree to pay $5 billion plus to get a new engine designed by a major.
Let's take a look of Chinese engines development timeline:
The WS-10 engine started testing on J-11A from 2002;
The engine only became mature enough (life time >300h) around 2010 and enter into massive production;
Then after 10 more years usage, PLAAF was confident enough about the reliability of WS-10 and put it on the single engine jet J-10 around 2020;
Finally, in 2023, we see the WS-15 appeared on J-20 for testing.
So, basically, it crossed 20 years from testing 3rd generation engine to testing 4th generation engine for Chinese.
Now, it is 2024, we haven't seen any Kaveri tested on a flying fighter jet yet.