"On time" would be any externally imposed deadline, and I would say it's completely the fault of imperfect estimation practices.
If we could estimate perfectly, then deferring all work until it needed would be uniformly good. But many times the true size of the work is unknown and we procrastinate on estimating, and we only figure out how much work is involved until it's too late.
What is "on time"? If things aren't getting done on time surely that is at least partly the fault of imperfect estimation practices.