All match markets are based on the result at the end of the regular time. This includes any added injury or stoppage time but does not include extra time, time allocated for a penalty shootout or a golden goal.
Unless the bet terms express otherwise, overtime is part of the wager. This is standard practice at a sports betting site, and they'll spell out the terms specifically in their rules and elsewhere on their apps.
Betfair is a British gambling company founded in 2000. It operates the world's largest online betting exchange. Its product offering also includes sports betting, online casino, online poker, and online bingo.