So it's almost been 24 hours since I was first able to plot reset, but I think I need more time. To get more time, do I sign onto my mayor account, change the time back and reset or must I change the 3DS internal clock instead?
As long as you didnt save with your new character, its fine to go back to your mayor and change the time when isabelle ask. Just dont go anywhere beyond 6pm and you're fine.
You don't need to change the time, you can keep resetting as long as you need to. But if you just don't want to lose that day, or want the villager to move in on that particular day, then yeah it's fine to use Isabelle (may be stating the obvious but go all the way back to 5:5x am on the day you invited the villager, not just earlier in the day you've been resetting)