If you were able to get Blathers yesterday, by donating 5 creatures to Nook, when you talk to him the first time, he should give you a DIY recipe for the vaulting pole so you can explore the island for creatures that he needs. Technically you can get it day one if you donated 5 creatures to nook before I think 6 am. That's when the day started for New Leaf, so I think it could be the same for New Horizons. If it's already past 6 in your town, you have to wait for Blathers to show up the next day I believe. You can put his tent down, but he won't arrive until the next day.