overlapping time in excel

Nurses can have overlapping timesheet entries in our patient care
software e.g.

07:00 - 09:00  2.0   client visit
07:45 - 08:15  0.5   phone consultation
08:15 - 09:00  0.75  phone consultation

Somehow the timesheet report in the patient care software calculates
2.0 hours *actual* time as well as 3.25 hours *total* time.

I'm pulling data through odbc to import into our payroll package but
my import file only computes the *total*, not the *actual* which is
what I want. (A start date/time column and an end date/time column for
containing each entry are in my worksheet). I'm not smart enough to
figure out if this can be done with a combination of functions or if
some vba could do this.

Thanks in advance.