TS: Ability to capture negative time

When users capture time it should allow them to also capture negative time.
The reason for this is:
I capture my time against request x = 5 hours
After month end has closed I realise it was the wrong number
I now want to capture -5 hours against that request to cancel the entry out and then add a new entry in the new month to rectify it.
An option is also to be able to tick the wrong entry and duplicate it to a negative but trust PPO will com e up with the best solution.