I think India's BMP and T90 replacement in the PPP arrangement will certainly take a lesser time compared to Arjun project for example. A lot has already been done in the Arjun and Abhay tech demonstrator.
If you want to an analogy, I hope Tejas, Arjun, Dhruv work out like Prithvi and Agni 1 to Shaurya, Agni 3+, etc. In the sense that the initial projects took a longer time, but the successor ones have a shorter developmental cycle. This is true to Dhruv to LCH example.
Either way, the grueling work these Indian scientists have done will be worth it in the next 20 years. India's military industry will be impressive by then.