Here's what you should know about TTing. The biggest fear is that a villager will move out without telling you, you don't have to worry about that because only one villager will be considering at one time. Since Cole already said he's moving, no other villager will move until he's outta there. About your flowers, if you TT backward a day, it'll count towards the countdown to Cole's move day. TT backward a year and it'll still count as a day. TTing back means wilted flowers will not die, and neither will they be revived if you water them. This means if you want to get to the 30th, his move out date, TT to the 29th, then save, then TT to the 28th and Isabelle should tell you that Cole's in boxes. Or just TT forward day by day and ensure all your wilted flowers are watered.