Change Size Of Range Dynamically

Need assistance with this code provided by SHG. See attached sample. I need to create a range called DaysOff so that this function will work. As it is the function is perfect; though the accuracy if the result is dependent on the exact range, thus I need this named range to be dynamic. I have tried but it does not seem to work correctly. The named range should refer to the list of names between 1-10. The range should dynamically include any names that are listed.

Public DaysOff As Range
Function datNext(datLast As Date, DaysOff As Range) As Date
Dim datBeg As Date, datEnd As Date
Dim iLastPd As Integer
Dim iDay As Long, nDay As Long
Dim iYr As Integer, iMo As Integer
iYr = Year(datLast)
iMo = Month(datLast)
datBeg = DateSerial(iYr, iMo + 1, 1)
datEnd = DateSerial(iYr, iMo + 2, 0)
iLastPd = Pd(datLast)
nDay = DaysOff.Rows.Count
Do.......................................