Time difference without weekends

[Egg 'n' Bacon]

We are trying to come up with a formula that will result in hh:mm (result cells are formatted as [h]:mm) between two date/times, that does not include weekends.

For example;
4th July 2016 10:00
minus
29th June 2016 16:30
results in 113:30 not 65:30

Any ideas?

[HansV]

With the start date/time in A1, and the end date/time in B1:

=B1-A1-(DATEDIF(A1,B1,"d")-NETWORKDAYS(A1,B1)+1)

[Egg 'n' Bacon]

Lovely, thank you