Calculate response time between 2 dates and time within business hours

Hi all,
I'm completely new to this forum and not that great MS Excel. I do the IT management for a company so a lot of different task ends up at my table. This is one of them.
P.S. My native language is not English but I hope you do understand me.

TASK:
To calculate the response time for our service jobs. From when we receive the call until we starts it.
This needs to be calculated based on our business hours. That also means holidays and weekends needs to be excluded.

I have attached a spreadsheet example and the columns we are interested in calculating is the "Required start date" and "Required start time" minus "Actual start date" and "Actual start time". The data in the example are put in manually (just for test purpose).

Our business hours are Monday-Thursday 08.00 to 16.00 and Friday 08.00 to 15.00.
We also have to be aware of dates changing from one month to another.

I have had a quick look at some other posts regarding this subject but can't seem to figure out how to edit the formulas so they fit to my needs. Some old posts have users like daddylonglegs who seems quite good at this.

I really hope someone can help me with the correct formula or lead me in the right direction.
Thanks in advance.

Please try in J5 and copy down

Formula:

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You are a genius!!!
Thank you SO much... It all seems to work perfectly

Now I will sit down and take your formula, bit-by-it, and understand it...it's quite a long one

Thanks one more time...you just saved me a lot of headaches.

=IF(F5*H5>0,
8/24*NETWORKDAYS.INTL(F5,H5,"0000111"): Counting workdays Mon, Tue, Wed, Thu * 8/24, because these days have 8 business hours
+7/24*NETWORKDAYS.INTL(F5,H5,"1111011") Counting workdays Fri * 7/24, because Fri has 7 business hours
-NETWORKDAYS.INTL(H5,H5,"0000111")*(MAX(0,MIN(8/24,16/24-I5))) Correction if Actual Starttime before 4:00 PM in cases of MON, TUE, WED and THU
-NETWORKDAYS.INTL(H5,H5,"1111011")*(MAX(0,MIN(7/24,15/24-I5))) Correction if Actual Starttime before 3:00 PM in case of FRI
-NETWORKDAYS.INTL(F5,F5,"0000111")*(MAX(0,MIN(8/24,G5-8/24))) Correction if Required Starttime after 8:00 AM in cases of MON, TUE, WED and THU
-NETWORKDAYS.INTL(F5,F5,"1111011")*(MAX(0,MIN(7/24,G5-8/24))) Correction if Required Starttime after 8:00 AM in case of FRI
,"")

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Thx again HansDouwe - you are a life saviour. I have now added reputation to your profile. This is just SO GOOD!!!

Thx for the feedback and rep. .