I guess that's true, but it's very rare that the departure time of a Rajdhani is changed drastically, specially from Delhi. The only example that I am aware of in recent years is 12432 TVC Raj, which was changed to 06:16 instead of 10:55, and that is from NZM, not NDLS.
Although, I guess the same thing can be said for Shatabdis as well. Major time changes are very rare for Shatabdis as well