They are the same

They could mean the same, depending on context. However, I could say, "You should complete this section of the test in twenty minutes", meaning "this part should be completed within twenty minutes" (but when you choose to start and end is not specified). If I said, "You should start in twenty minutes time", it means you should start twenty minutes from now (at that specific time).

I'm pretty sure it means the same thing. Just ２different ways of saying it.