Well, there are several combinations
- Isn't it time you did/went/… = Isn't it time when you did/went/… you ask if some past event had happened simultaneously with another past event
Perfectly, it should be: Wasn't that happening at the same time/during the period/at the moment when you lost your car? =>. Wasn't that (at the/in) time when you lost your car? => Wasn't it time you lost your car? => Isn't it time you lost your car?
(It is time when I was young. Present, is, that is here, and in the above example, is reviving the past or just a direct instructive question someone asks: Is it true that you spent all your money?)
Not to forget the other usages
- Isn’t it time that this program is going to squander far beyond our expectations?
Is this program going to spend a lot of time to start and execute because it is so slow? or Is this program going to spend a lot of time to be developed because it is very complex?
This additional usage I added to say that time could mean a quantity of time.
Isn’t it time that this program is going to squander far beyond our expectations? => Isn’t it a (large) quantity of time that this program is going to waste far beyond our expectations?