Hi, I don't know if you have solved your issue by now, but I guess not since PhilFrisbie's comments don't really help.
I just had the same issue with a time which was 3.89 in field C4
So I used: =FIND(".",C4) that returns me the position of the . which is 2
=Left(C4,D4-1) which returns me 3
=right(C4,D4) which returns me 89
Just multiply 89*0.6 and you have minutes
I tried to do it by using the function =split() but couldn't make it to work on a calculated field.