Playing games with times in Excel is one of the least fun things you can do this side of the Tory Party conference.
Yes. As timelord for our local club TT series, I have to wrangle times in a spreadsheet quite a lot.
For me, the biggest issue was that excel can't handle negative times by default.
And I need to.
I need to calculate veterans's times against a 'standard', and they can be plus(faster) or minus(slower) than the target time.
The underlying reason is that excel converts anything that looks vaguely like a time into a 'serial number' under the hood. This is I think an un-signed integer. This serial number is then displayed back to you in the format you select in the cell formatting. Due to the underlying data being un-signed, it can't go negative.
The solution is to set the spreadsheet to use the '1904' date system.
This applies an offset, or bias, to the serial numbers, allowing us to go negative by up to (I think) 4 years.
(You need to set the date system in the first instance, before entering any dates/times, otherwise it re-interprets the existing serial numbers and then displays them as 4 years out! A work-around is to export the column of dates/times as text, then re-import them once the date system has been changed.)