Conditional formatting for [h]:mm time format

Hi

I have a spreadhseet that has time in the format [h]:mm and I am calculating the difference between planned and actual time.

If the variance is less than or equal to zero, I want it to go green and if it is greater than zero, I want the cell to go red. The answers for the variance are in the same format of [h]:mm

Example:
Duration Planned Time Variance
2:00 1:50 -00:10
1:00 0:55 -00:05
2:30 3:05 0:35

Any help would be appreciated