"It's about time" is very commonly used to indicate something is past due:
(it is) past the time when something should have happened: It’s about time she got a job.
It's mildly sarcastic, because the other meaning is that it's the proper time:
Long past the right time; also, approximately the right time.
If I say to my family, "Finish up whatever you're doing; it's about time for dinner," there's no sarcasm implied. If my family says to me, "When are we eating? Isn't it about (or around) dinnertime?" That isn't sarcastic.
If my family says to me, "It's about time you serve (or served) us dinner!", that is sarcastic, and I might invite them to try cooking their next meal themselves.
Note that "it's about time" is often followed by the past tense:
- It's about time that our country invested in education.
- Enough of this guy, it's about time he stopped this nonsense.