DayBack will attempt to auto-detect date and time formats automatically. If it isn't detecting it properly or you need to change it here's how:
Visit "Administrator Settings" and you'll see a section for Time Formats. You can replace "auto" (the default) with a specific format: the notation for 12 hour format is hh:mm a
Note that these time formats as case sensitive: "H" is the notation for 24 hour format. You can find all the available format notations here: https://momentjs.com/docs/#/displaying/