Well, there is a difference in certain contexts. If you were to say "It's time to do action" it wouldn't make any sense. But, if you said "It's time for action" it would.
Another example would be, "It is time to do laundry" would be correct usage of English. But, if you were to say, "It is time for laundry" It might sound a little strange. Also, if you want to sound more fluent, shorten up the "It is" with "It's". It really makes a difference in sounding like a fluent speaker.
Also figuring out the right times to fit "The" in a sentance makes a difference. Like for example again, if you said "It is time to do laundry", it wouldn't sound as fluent as if you had said: "It's time to do the laundry".
Just a few pointers there. If you have any other questions feel free to ask.