TSA knows who you are way ahead of time when you put your secure flight information in, and maybe it checks the information when your boarding pass is printed. Airlines close check-in so they don’t have unexpected people showing up during boarding. But if you get rebooked on a different flight or something, they can check you in at the gate whenever.
Also, United and Delta let you check in 30 minutes prior to departure if you don’t have bags.
You must checkin no later than 45minutes before your flight. It’s a TSA requirement so they can confirm the manifest
I’m guessing that’s a USA-only rule.
The TSA doesn’t have much authority over other countries
It’s all there in the name: the Transportation States of America
This is the only real rule. Some airlines will have incentives for checking in early.
EDIT: a little bit of research seems to show varying times down to as low as 30 min, and up to about 90 for international travel.
TSA knows who you are way ahead of time when you put your secure flight information in, and maybe it checks the information when your boarding pass is printed. Airlines close check-in so they don’t have unexpected people showing up during boarding. But if you get rebooked on a different flight or something, they can check you in at the gate whenever.
Also, United and Delta let you check in 30 minutes prior to departure if you don’t have bags.
Why would the TSA care about when I check in?