Changing the time on the phone would work for your personal call history but not the official call history that shows on your phone bill.
As a father, I check my kid's phone calls and minutes semi-regularly by logging on to T-Mobile and viewing their recent activities.
Now, chances are if you need this for an alibi for a GF or some other friend it will work. If you need this for a more serious alibi, it's not going to work if the person has any way of checking the official carrier records.