Durations are easiest to count in minutes, and easiest to read in hours. 450 minutes is 7 h 30 min: RoundDown gives the whole hours and Mod the minutes left over. As decimal hours, the way payroll usually wants them, it's 7.50: divide by 60 and format with Text(..., "0.00").
Power Apps has three functions that round a number to the decimal places you choose. Round goes to the nearest value, RoundDown always goes down and RoundUp always goes up. 445 minutes is 7.4166… hours: Round(445 / 60, 2) makes it 7.42.
Mod returns what's left over after a division. Mod(450, 60) is 30: 450 minutes is seven whole hours with 30 minutes left over. Together with RoundDown for the whole hours, it turns a number of minutes into hours and minutes.
TimeZoneOffset tells you how many minutes the user's local time is from UTC at a given moment. Add that number to a local time with DateAdd and you have UTC: in London, 09:00 on 1 July is 08:00 UTC. Pass the moment you're converting, because daylight saving changes the offset.
Twice a year, a night shift is not the length its clock times suggest. When UK clocks go back in October, 22:00 to 06:00 is nine real hours; when they go forward in March, it's seven. Build the start and finish as real moments with DateTime and count minutes with DateDiff, and Power Apps counts the real time on both nights.
A shift from 22:00 to 06:00 lasts eight hours, but on one day's clock 06:00 comes before 22:00, so a plain subtraction goes negative. When the finish time is earlier than the start, put it on the next day, then count the minutes between the two moments.
DateDiff measures the time between two dates or times, as a whole number of the unit you ask for. Ask in hours, and 17:00 to 20:30 is 3: the half hour is lost. Ask in minutes, get 210, and divide by 60 for 3.5 hours.
DateAdd adds an amount of time to a date or a date and time: a day, a few hours, 450 minutes. Give it a negative number to go back instead. It's how a timesheet moves a finish time onto the next day.
A date picker gives you a date, a time picker a time; many things need both, as one moment. DateTime builds it from the parts: DateTime(Year(d), Month(d), Day(d), Hour(t), Minute(t), 0) is time t on day d.
Hour and Minute take a time apart. For 22:30 they return 22 and 30, as numbers. Hour always counts on the 24-hour clock, from 0 to 23, whatever format the time is shown in.
