Isn't it about time you left the hospital?
Isn't it about time you leave the hospital?
Isn't it about time you forgave yourself?
Isn't it about time you forgive yourself?
We are dealing here with two different constructions which carry quite different nuances of meaning. 'Isn't it about time you left the hospital', is fine. It also carries at least a vague note of censure to the listener.
This first example is nearly always used with the past tense. One exception I can think of is with 'could'. 'You are thirty-five years old. Isn't it time you could drink through a straw?'
I think the second example needs to read. 'Isn't it about time for you to leave the hospital'. I am not sure it is grammatical without them. But that sentence does not contain the same hint of reproof.