See exactly what delaying your SIP start by a few years costs you by the same target date.
Cost of delay: SIP value if started now − SIP value if started later, both ending at the same target date
Does delaying always cost this much?
The cost scales with your assumed return and how early in the investment horizon the delay happens — a delay near the end of a short investment period costs far less than the same delay at the start of a multi-decade one, since there's less remaining time for the missed contributions to have compounded anyway.