In Properties Goto--> Dimensions-> Calculated Dimension
use following Expression as if(Late(mm)=0 and Late(mm)='-','Total elapse time',Late(mm))
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You can use Alt();
=Sum(Alt([late (mm)], [Total elapsed time])) to replace nulls with the elapsed time values.
I see you want the zero values converted as well. In that case
=Sum(If(len([late (mm)]) = Or [late (mm)] = 0, [Total elapsed time], [late (mm)]))
I am assuming that the '-' are null values.