When time passes by, you say it elapses. Four years elapse while you are in high school. Nine months elapse while you are in the womb.
If two weeks have elapsed between your tennis lessons, there has been a two-week lapse between sessions. The word elapse comes from the Latin word elabi which means "to slip away." Time is one of those things that really does tend to slip away, unless you're sitting through a lecture on the nature of time. Then, it might feel like years elapse when really it is just a few minutes.