Manipulating ranges in a different file

Hello,

My excel file collects information from another excel file, where I
have three columns: start_time, end_time, and another cell that is
suppose to contain a name of the person. Within one range (3-250) I
need to subtract end_time from start_time and see if it's less than 16
minutes, if so, if the third cell, does not contain the name, I need
to count all the occurances and record the number into the cell of the
correct file.


I cannot quite figure out how to perform subtraction within the range
(in this case: column G - column F):

=SUMPRODUCT(--(('path[FileA.xls]Tab1'!G3:G250 [...???...]
TIME(0,15,59))*(LEN('path[FileA.xls]Tab1'!Q3:Q250)=0)))

Thanks a ton for your advice!