People can change their vote up until the closing of the vote, which can be delayed even after all votes are cast, basically until Johnson decides to close things. Vote flipping is pretty frequent as congressmen get bribed or persuaded one way or the other.
Speaking of Johnson, he just voted yes despite tabling the vote multiple times over the year including adjourning congress for weeks-long breaks and avoiding swearing in Grijalva for over a month completely against precedent.