Format cell for displaying negative result when summing time format

Birgir_F 

1. click File tab, and select Options from the menu list. And the Excel Options dialog will open.
2. click Advanced from the left pane, and check Use 1904 data system under When calculating this workbook section. Click Ok button

Another option is to make-up it by using TEXT() and MAX() and MIN() formulas if you want it  time formatted (HH:MM)

=TEXT((MAX(Q35:Q36)-(MIN(Q35:Q36)+K37)),CHOOSE(N(Q36<Q35)+1,"-[H]::MM","[H]::MM"))

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