Except for those things that are recited in prayers, a follower must perform all other acts of the prayer – such as the rukūʿs and sajdahs – either with the imam or a little after him. If he intentionally performs them before the imam or delays them after the imam to such an extent that it cannot be said he is following the imam, his congregational prayer is invalid.
However, if he acts according to the duty of one who performs the prayer on his own, his prayer is valid as per the details that were mentioned in