Assume times are entered in A1 (first time) and B1 (second time).
C1: =IF(B1>A1,"- ","+ ")&TEXT(ABS(A1-B1),"[hh]:mm")
That being said, since it is now a text cell, in order to manipulate this
time, you would need something like the following.
Assume cell B3 has time that needs to be modified by your time in C1.
C3: =B3+MID(C1,3,LEN(C1)-2)*IF(LEFT(C1,1)="-",-1,1)
It works....
