Brakes off to brakes on.
If it goes over by 15 minutes, you log 1:15. If you land five minutes early, you log 0:55. (Opinions differ as to exactly how, most commonly to the nearest five minutes, next most common is "decimal time" so to the nearest six minutes: e.g. 1.1, 1.2, 1.3, etc., a few people - mostly glider pilots log to the nearest minute).
And, most places, they'll charge you for that as well. Expect to pay for what you actually fly, not what you book. If you will have trouble paying for over the booked 60 minutes, make sure that your instructor knows that in advance.
You really need to talk to your flying instructor more!
G
(Nowadays I log to the nearest minute, but managed the first 22 years of my flying career logging to the nearest five minutes quite happily.)