Are both Startdate and Enddate in numerical date format, or as strings? For a quick check, create a list box for each field and check the alignment - if left aligned they are string values and you need to convert them to dates (preferably when you load them).
Date(Date#(Startdate, 'yyyy/MM/dd hh:mm')) as Startdate,
Date(Date#(Enddate, 'yyyy/MM/dd hh:mm')) as Enddate,
(change the fomat string to match the format of the string values)
Then the syntax you used should work.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein