Was it legal for the kicking team to advance the ball on an onside kick at anytime in the nfl?

Yes, it is legal for the kicking team to advance the ball on an onside kick in the NFL, but only under specific conditions. The ball must travel at least 10 yards before the kicking team can legally recover or advance it. If the ball does not travel the required distance, the kicking team cannot advance it and the receiving team gains possession at the spot of the kick.