As for Groundhogs you've already captured and tamed, you'll be able to keep those as pets even after that date. If you're looking to capture a whole herd of them, however, you'll need to plant lots of crops, and fast, along with setting out your armed Groundhog Traps (the more the better at this point) in order to catch the number that you want.
Remember, you can also share your trapped Groundhogs on your news feed if you choose not to keep them as pets. If you've not been lucky enough to capture Groundhogs of your own, why not keep a lookout to see if friends are sharing any extras that they've come across?
How many Groundhogs have you captured and kept as pets? Let us know in the comments.