Doing calculations on date/times is tricky, because there are a lot of other parameters that you usually don't think about. Are the two times in the same time zone, for example? Or on which date are the two times?
I see that you want
22 hours + 22 hours to be displayed as
1 day + 20 hours, which sounds reasonable enough, but that assumption fails as soon as a day is not 24 hours - as it can be, when going from/to daylight savings time.
So I think the best you can get is to show the number of hours (
44). However, it does not make much sense to format the sum cell as a date (which date? January 1st?), but as a duration:
Feel free to look at/copy the example spreadsheet I've set up.