Hello Darren,

when I use that formula using cords' example dates I get a result of 54.83. I think that's 24 hours too little, the total hours between them is 126.83, with 2 weekend days so shouldn't the result be 78.83?

This version should give the correct hours, I think

=IF(NETWORKDAYS(A1,A1)+NETWORKDAYS(B1,B1)<2,B1-A1,NETWORKDAYS(A1,B1)-1+MOD(B1,1)-MOD(A1,1))*24

where start date/time is in A1 and end date.time in B1

format result cell as number

It counts all hours between A1 and B1 if either of the dates is at the weekend, otherwise it excludes weekends