When you use Max or Min on a date Qlik will remove the text format of the date and just keep the numeric part. So be sure to wrap the Max and Min in a Date()-function to reapply the correct time format:

vFromDate = Date(Max(FromDate));

vToDate = Date(Max(ToDate));

The expression should then be:

=If( BusinessDate > vFromDate AND BusinessDate < vToDate,BusinessDate )

or

=If( BusinessDate > '$(vFromDate)' AND BusinessDate < '$(vToDate)' ,BusinessDate )