=SUM(IF((C3>J$3:J$50000)*(B3<K$3:K$50000)*(A3=I$3:I$50000),((IF(C3<K$3:K$50000,C3,K$3:K$50000)-IF(J$3:J$50000>B3,J$3:J$50000,B3))*24*60),0))

Formula above is set as an array.

Column C contains end date and time (e.g. 3/6/16 0:30:00) of a schedule pair.
Column J contains start date and time (3/5/2016 0:01) of LogInLogOut pair.
Column B contains start date and time of a schedule pair.
Column K contains end date and time of a LogInLogOut pair
Columns A & I contains employee IDs.

Please explain exactly how it works because while I understand that the formula basically sums the minutes that fit within the schedule, I don't know how it does that in a step-by-step manner.

Thanks in advance!