If you get back in/on time, you can come with us.

[thehammer]

When should I use 'on time' and 'in time'?

- If you get back in/on time, you can come with us.

 

[emsr2d2]

It depends on what you want to say. If you've given the person a strict deadline by which time they must be back, then it's "on time". If you simply mean that they can come with you if they arrive before you leave, use "in time".