Does a rak'ah count for someone who entered the mosque and stood [in prayer] five seconds before the Imam bowed, after searching for a spot?

To catch a Rak'ah with the Imam, one must join him in bowing (Ruku'), meaning the congregant bows with the Imam before the Imam rises from Ruku'. The sufficient degree of bowing is to incline oneself such that one's hands can be placed on the knees. If you join the Imam at this point, the Rak'ah is counted for you. If you do not join him at this point, it is not counted for you.