In my opinion (as a new member with no connection to TurboTax other than trying to make it work), you can use one date.  The date has zero impact on anything other than the pain in the *** it is causing users.

There are much bigger issues with using T5008 slips to report Capital gains on non-Canadian stocks.  Hopefully when TurboTax gets around to fixing the bigger issue, it can improve it's user experience in entering T5008 information.

The biggest pain is having to enter the same information for each and every T5008 slip.  One should be able to specify the use of all of the T5008 slips as Capital gain (not enter this dozens of times).  Same with the Spouse  percentages and a default disposition date.

I no longer trade like I used to - in the past I must of had close to one hundred T5008 slips.  Back then I do not recall it being as bad.