I think mine were planted late July and so calculated they would be ready towards the end of October beginning of November. The plan was to leave a couple of bags for harvest in December I didn't expect them to grow as quickly as they did though. Last year they were planted later and didn't grow to a sufficient size before frost got them and the bags froze solid.
...they've reached this far against all odds, first strong winds damaged foilage before I'd put in supports, slugs and caterpillars have had a nibble at the leaves, they've been saturated with an on slaughter of continual rain..you could count the number of times I've watered them on one hand and now me thinks they have late blight as the stems are slowly going brown
I was putting off delving into the bags to check if they are ready as I'm still eating spuds harvested June/July time. I'll check them tomorrow. Don't suppose they can be left in the bags if they have blight?