It's been a couple years since I played roulette in the US, but in the UK/Europe you can definitely still place bets for a few seconds (maybe 5?) after the ball is released.
I've played roulette for the past 2 years at several casinos in the US and you can still place bets after the ball is released. Once the wheel starts to slow down and before the ball drops onto the wheel, the dealer will signal no more bets.