Using dates & times in Excel is a doddle, if you're willing to take a little time to learn it. Sometimes the automatic formatting works, sometimes not - so you may as well get used to doing it manually, then you always know where you are. Handy shortcut key: Ctrl+1 brings up the cell formatting box.
It also helps to remember that in Excel's internal representation, a day = 1, so an hour = 1/24 days, and so on. That has to be correct before the formatting will look right - if it all seems bizarra, check it by going back to "general" format.