Hi Prets

Have a look at the attached file. if I understand you correctly, as long as their shift includes the 4hrs 00:00-04:00, they get the night shift rate!

So in column G of the attached sheet is a IF function returning "Extra Payment" if they worked those hours, using the small table in L1:N3.
I have also included a column for payment using a nominal hr/rate (J2).

You might have to adjust the formula, as I might have misunderstood your post. I have paid them the shift plus an extra 4 hrs at £1.50 ph. This can be adjusted in the formula to pay an extra 1.5 for each hour if required.

Hopefully this is of some use!