Excel Formula

[Icarus]

Seems you maybe making life difficult for yourself. Is there a reason for not wanting to use two columns, one (Column-A) for HH and the other (Column-B) for MM.

Then you could:

SUM(Ax:Ay) + INT(SUM(Bx:By)/60) for HH
and
MOD(SUM(Bx:By),60) for MM.