In compounding mathematics, the money generated in the final years dwarfs the early contributions. Postponing your monthly SIP by even 1 or 2 years cuts off the highest-compounding years from your portfolio horizon.
Waiting 12 months before starting a ₹10,000 monthly SIP costs you only ₹1,20,000 in missed contributions, but costs over ₹12,00,000 to ₹18,00,000 in lost terminal wealth over a 20-year horizon.