I'd use something like this
Count(If(entryDate = Date(Now(2), 'YYYY-MM-DD hh:mm:ss'), returnPartyId))
The 2 as a parameter of Now() will return the time when the document was opened. Using 1 will return the current system, time, but will be updated every second, that means that the chart will be evaluated every second, and that will slow down your system. There are other functions such as LocalTime() and Today() that work very similar (updating every second).
Hope that helps.