I would guess that he’s trying to use the time period in the IF condition, such as “IF the time is between midnight and sunrise, and a motion sensor trips, THEN turn on a security light and send a notification” or something to that effect. Not sure that you could accomplish that with two routines.
The UI sucks because it looks like you can choose “Period of time”, then select Start Time and set it to midnight (on the Time tab) and then select End Time and set it to Sunrise (on the Day Tab), but if you click on the Day or Night tabs it automatically switches both the Start and End Time to be of the same type: Time, Day, or Night.
For a period of time, the Start Time and End Time should be independent types. You should be able to start at midnight and end at sunrise; but you cannot mix and match.
That UI is buggy for other reasons too… like it shows Day is sunset to sunset (instead of sunrise to sunset) and it shows Night is sunrise to sunrise (instead of sunset to sunrise).