Convert Array Formula into VBA User Defined Function

I want to convert the below count & if function into a user defined function. However, its outcome is false. What's wrong with it? Can someone helps?? Thanks in advance!

Public Function TestFunction()

Result = Selection.FormulaArray = _
        "=COUNT(IF(Data!R2C3:R9999C3>R1C,IF(IF(Data!R2C1:R9999C1>R[-1]C1,Data!R2C1:R9999C1)<=RC1,Data!R2C3:R9999C3)))"

TestFunction = Result

End Function

Thanks Joseph! The reason is I want to hide my calculation. I have to let the user to know the raw data but cannot let them know to calculate it!

I have changed my code but the outcome is still "FALSE". Are there any problems?

Public Function TimeGroup()

TimeGroup = Evaluate(ActiveCell.FormulaArray = _
        "=COUNT(IF(Data!R4C3:R9999C3>R5C,IF(IF(Data!R4C1:R9999C1>R[-1]C2,Data!R4C1:R9999C1)<=RC2,Data!R4C3:R9999C3)))")

End Function

The code is obtained from Macro recording but it doesn't work in module.

I want to use a User defined function to replace the formula in the spreadsheet "Master Table" of the attached file.