The perfect time to put up Christmas lights depends on a few factors. If you want to enjoy the lights during the holiday season, it's best to put them up before Thanksgiving or early December. This way, you'll have plenty of time to enjoy them before the big day. However, if you prefer to wait until closer to Christmas, you can put them up as late as mid-December and still have them up in time for Christmas. Ultimately, the choice is up to you and what works best for your schedule and preferences.