This works for me in a simple spreadsheet I made for work to calculate flight times from wheels off to wheels on. It sums the individual flight times as well.
Wheels off & on cells (A1 & B1 respectively): format as time eg 13:30
Sector time (C1): format as custom [h]:mm
formula is: =IF(b1<a1,b1+1,b1)-a1
Total times (cell C10): format as custom [h]:mm
formula is: =sum(C1-C9)
Note: You must enter the times with a colon divisor eg 14:34, not 14.34.
The sector time works as follows:
=IF(wheels on < wheels off, wheels on+1, wheels on)-wheels off.
Translated: IF 'wheels on' is less than 'wheels off' add to it 24 hrs (a single day ie '1') then subtract 'wheels off' from 'wheels on'. If 'wheels on is NOT less than 'wheels off' then subtract without doing the previous 'add a day' thing.
This correctly calculates the time even if the arrival time is after midnight. An arrival time after midnight means the time is numerically less than the departure time. It's not really since the time has moved forward by a day. Excel stores date/times as a whole number+decimal fraction. The whole number is days, the decimal part is the hour/minute/second fraction of a whole day.
Starting on day '0', 12 midday would be 0.5, a day later 1.5, 2 days later at 6pm would be 2.75 etc etc.
If you want to split the hours & minutes for some other manipulation then you can use the =HOUR(cell) & =MINUTE(cell) functions. These two refer only to the numerical value of the hour or minute component of a time.
You could then use the minutes fraction to derive a decimal fraction of an hour, then add the decimal back to the hour fraction. There's probably a function in Excel to to that directly since it already stores time as decimals.
You'd still have to use the ROUND function to round to the nearest tenth. Something like
=(hour(D1))+(round((minutes(D1)/60*100),1))
I've not tested this but it would be something similar. I've used something like it to calculate the expected fuel burn for the sector.