Can't remember which sheet I took that example from but details for one of
the sheets are as follows :-

C89 = 5:30:00 a.m. which displays as 5:30 because of the [h]:mm
D89 = 6:51:00 a.m. which displays as 6:51
E89 = =IF(C89 <"",IF(D89 <"",+D89-C89,"no finish time"),""), which gives a
result if I F2, F9 of 0.05625 but displays as 0:00

I've tried reformatting and recalcing E89 in various ways, but all give a
display of 0 in various forms.