I am not sure of capability that user can enter data.
alternative will be in your script create a table(calendar) that has all the dates. Use a filter in front end give user a capability to enter or search date in there. make sure your Date column name in calendar table matches with your EntryDate.
Then Your KPI expression would be
if(GetCurrentSelections(EntryDate1)>=EntryDate1 and GetCurrentSelections(EntryDate1)<=DueDate1,Name,0)
may be it helps.