Hey @nathanu! 😄 Super awesome hike you've got planned! I did the AT with my dog in 2011 and skipped the approach trail because I didn't want to deal with a dog on leash in a crowd; going back and doing that 8 miles is on my bucket list! Even though it's a slog of a climb, I've heard it's absolutely beautiful with the waterfall views. Have fun on it! 🙂
The best piece of advice I can offer is to keep your pack weight low. You're just going to be out for one night. I don't say that to minimize/discount your trip (please don't read it as "You're just going to..."), but rather to remind you that you'll be back at your car the very next day so there's no need to pack two pairs of pants, three socks, etc. Especially if it's going to be raining, consider leaving the camp comforts behind: the one pound chair, hatchet, etc.
One piece of advice I could give would be to check what time sunset is. Let's assume it's 6:30. I prefer to stop hiking one hour before sunset, which would stop me hiking at 5:30 to give myself time to set up my tent, cook supper, gather water for the night, etc. Do a pace audit on yourself at the last potential alternative campsite. Based on your start time and hiking pace, can you make it to the final destination campsite before that one hour mark and/or sunset? If so, great, push on. If not, maybe think about stopping for the night at the alternate and waking up early the next morning to finish your ascent. I think you would have plenty of time the next day to finish the up and then head back to the car, as most people hike faster on the downhill than they do on the uphill. 🙂
Eat a good breakfast to give you enough energy for the stairs, and drink plenty of water (especially if it's raining - we tend to forget to hydrate ourselves if there's water all around us).
And, most importantly, don't forget to come back and share photos of your accomplishment! 🙂 Happy trails!