RIGHT("0" & (SUM(Fields!TotalTimeSpent.Value MOD 60, "Group3")), 2)
Value is 273, I am getting 93 returned instead of expected 33.

expressions purpose is to calculate time spent, here is the complete expression. This works on almost all entries, this is the only example I have seen where it is adding the values instead of modding.
= IIF(FLOOR(SUM(Fields!TotalTimeSpent.Value / 60, "Group3")) = 0, "00", FLOOR(SUM(Fields!TotalTimeSpent.Value / 60, "Group3"))) & ":" & RIGHT("0" & (SUM(Fields!TotalTimeSpent.Value MOD 60, "Group3")), 2)
Did you perhaps mean to do the MOD calculation after running the SUM? So the expression would be:
As a test, if I run just:
It gives me the expectedresult of 33.