The two important forms are the following: 1) "It's about time" + infinitive (or Object + infinitive) "It's about time to go home." "It's about time for her to go home." Both of these are just stating that the time for the action has arrived. The second one, said in a funny or mean way, could mean that you really want her to go home / go away. "It's about time for her to go home. I'm so sick of listening to her." 2) "It's about time" + past verb = subjunctive: This gives the speaker's opinion, feeling, recommendation or wish about the matter. It's NOT a real past time situation. "It's about time she went home." (Could also be said in a mean way.) "It's about time you sold your car." "You've been sitting around all the time playing video games and eating all of the food. It's about time you went out and found a job." "It's about time you find a job" and "It's about time you sell your car" are also possible but not really formal / correct English (don't choose these on tests) : ) I wouldn't use the present tense, but many Americans would. I don't know how that sounds to non American English speakers. It´s about time to went home.*** This one is not possible in formal or informal English. It's just wrong. In general, the infinitive means "now is the time" and the past subjunctive means "it's already a little late" and I think that's why it shows the speaker is bothered in a lot of situations. (That's just my opinion, though.) "It's about time you sat down and prepared for those exams. How do you think you're going to get into the university?" (A parent arguing with a child, perhaps) You can add "high" to be more emphatic: "It's high time you started paying your own way. I can't afford to have you borrowing money off of me."

I totally agree with srgause, however if these sentences were said in a sarcastic tone, then the meaning would change.

I'll define "it's about time" by each group, since the meanings are similar: It is about time for her to go home. It is about time she went home. It is about time she goes home. All of these mean it's the right time for her to go home, or she should have gone home much earlier. It is about time to go home. It´s about time to went home. These aren't correct. Maybe you mean It's about time I went home? That would mean it's the right time to go home, or I should've gone home much earlier. It is about time you sell your car. It is about time you sold your car. Both of these mean it's the right time to sell your car, or you should have sold the car much earlier. I often hear this phrase in the sarcastic sense, meaning that whatever is happening is long overdue. example: It's about time you cut your hair (meaning my hair is a mess and should've been cut a long time ago)