Business Hours between 2 dates/times excluding weekends and holidays

We have a system that tracks the beginning and ending date/time of customer inquiry tickets opened. I need to be able to track how many business hours it is taking to close a ticket. Our bus hours are from 8AM to 8PM Monday through Friday, and we are closed on holidays.
Example
Cust Ticket opened date/time 2/8/2019 14:00
Cust Ticket closed date/time 2/12/2019 15:28
When i manually calculate the time, I get 25:28 [hh]:mm. Unfortunately, we receive over 300 tickets each week so manual calculation is impractical. Is there a formula that would provide the duration, in business hours, that it took for us to close the customer's ticket?

Any help would be greatly appreciated.

That could be shortened to

=(NETWORKDAYS($A2,$B2,$Z$1:$Z$20)-1)*("20:00"-"08:00")+MOD($B2,1)-MOD($A2,1)

without compromising functionality.

The addtitional networdays functions in post #2 will never result in anything other than 1, so are not needed.
The median functions would only be required if there is a need to adjust any times that are outside of normal business hours up or down to the closest start or end of day.

This is perfect - thank you! And yes, we receive tickets 24 hrs a day and so start/end datetime is often outside of the working day. The only adjustment I made was to begin with the condition that if starttime>endtime, "" - weird but happens every now and then.

Much appreciation for your help!!

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Glad the solutions provided work for you.

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