While studying asana or zazen, just sitting is said to be enough. However, most of us will agree that it never quite works out that way. Either the inner timer goes off and you are ready for something new and exciting or a thought pops in and diverts your entire direction.
Either way, giving your mind a rest is part of yoga practice just as much as twisting yourself into a pretzel and stretching out internal organs. Believing firmly in the perfect rest of our mind, we should resume our calmness of mind.
Take your time today, enjoy the flow, and allow your mind to just mellow-out. No limits.