Subtracting Date & Time taking into account NETWORKDAYS

Hi all!

Bit of a head-scratcher.

I am looking to put together a tracker for project submissions. It's a touch non-standard in that we need to take into account Days, Hours, Minutes & NETWORKDAYS.
So data wise I have two columns.

Column A) Deadline Date. Column B) Submission Date.

Both fields contain date and time (for deadline the time is always 12:00). What we need is a formula that will calculate the difference in time between the two fields, preferably split DD:HH:MM:SS but one that also takes into account NETWORKDAYS (as we have weekends AND holiday to factor in) so that we can ascertain how late a project is.

I enjoy an Excel challenge but this one has me beaten at the moment. I’m not even sure it’s possible without ramshackling a few cells together. Anybody have any ideas?

Hello can you please attach a file? I'm sure someone will come up with a solution here.

Do you have to factor in any working hours?