I have a spreadsheet among the colums are two that work out flexi time
accrued in either a positive or negative quantity,the cells are
formatted as time, I have got it working to a point, but now I have 35
minutes in the negative column that I want to add 44 minutes to in
other words it should read + 9 minutes I have been using this formula
whichh has worked OK untill I try to take 35 from 44 and get a + 9 value
where cell n8 has the negative amount and m9 has the positive below is
the formula I have been using

=IF(TIMEVALUE(N70),TIMEVALUE(N8)-TIMEVALUE(M9))

M N
6 3:41
7 00:57 2:44
8 02:09 0:35
9 00:44 ?:??
10 00:48

TIA
Parlo