For example, current time is 10:10.
then when will the train leave?
The train will leave in 10 minutes.
The train will leave in 10 minutes' time.
The train will leave after 10 minutes.
If the train leave at 10:20, what can we say?
For example, current time is 10:10.
then when will the train leave?
The train will leave in 10 minutes.
The train will leave in 10 minutes' time.
The train will leave after 10 minutes.
If the train leave at 10:20, what can we say?
In answer to the title's What is the difference:
The train will leave in 10 minutes.
Ten minutes from now, the train will leave.
The train will leave in 10 minutes' time.
Same as above. The extra word "time" is redundant, really, unless the audience doesn't know that minutes are a unit of time.
The train will leave after 10 minutes.
This one is a bit less clear. It implies that there will be some event, at some time, and ten minutes after that the train will leave.