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it would be best to see an example of what you're currently doing/ using to prepare your formula, however, you could create a formula that determins whether or not the day is Sat or Sunday and from there create separate formulas for if Sat is Less Than or Equal (LTE) to 2 multiply by 1.5 then take remainder times 2 (double time); and for Sunday multiply by 2 for double time.
Using the "= Weekday" formula, you can determine what day it is (helping you get the sat or sundays you need and corresponding multipliers. OR at time of entry you could have 2 separate columns on Sat (one for the LTE 2 yours and the other column for the remainder if any).
Ball is in your court!
if you found this useful, please give credit. Hopefully this also gives you some ideas as well.