I am flying transatlantic in a few days ex USA. Is the T-30 to select seats definitive? It's important since even business class requires payment these days to select seats and I boycotted the extortion.

One reason that I am asking is because I remember being able to check in / select seats way before T-22 when that was the official time 12-14 years ago when I used to fly intra-Europe a lot. For example, if I had a flight on the 31st, I could select a seat just after midnight between the 29th and 30th. I forget if it depended on whether the flight on the 31st was in the morning or afternoon.