The value you get by taking the difference of two timestamps is not a timestamp, but an intervall - and that intervall cannot be inserted as just hours - a timestamp is a defined moment in time, not an intervall - as I mentioned here you are simply using the wrong type for that column.
Please stop spamming the monastery with your rubbish postings - read
and please above all, read the documentation for the tools you use, namely MySQL in this case, and try to understand the problem you are about to solve before you come up with solutions that aren't likely to work because you don't understand the problem at hand - that seems to be the case here.
I'm a bit fed up with your behaviour here - posting, multiple times, without content, in the wrong sections, creating new accounts to make the same mistakes again - you are misusing a wonderful place, and with that you are taking away from yourself the opportunity to learn something from all the wonderful, helpful poeple here - kind of sad...
An intellectual is someone whose mind watches itself. -- Albert Camus