7s WR variation does not change the written law for offside:
19.28:
Prior to the start of play in the scrum, the scrum-half of the team not throwing in the ball stands:
a) On that team’s side of the middle line next to the opposing scrum-half, or
b) At least five metres behind the hindmost foot of their team’s last player in the scrum and remains there until the completion of the scrum.
Then
19.30:
Once play in the scrum begins, the scrum-half of the team not in possession:
a) Takes up a position with both feet behind the ball and close to the scrum but not in the space between the flanker and the number eight or
b) Permanently retires to a point on the offside line either at that team’s hindmost foot, or
c) Permanently retires at least five metres behind the hindmost foot.
And then the scrum ending doesn't change (except the No 8 reference is removed - ironically from law 19.36b but not from 19.36c) - so ball is out when it comes out past the last feet, or when the scrum half plays it.
19.33: As soon as the scrum ends, offside lines no longer apply.
19.36: The scrum ends:
a) When the ball comes out of the scrum in any direction except the tunnel.
b) When the ball is played by that team’s scrum-half.
c) When the number eight picks up the ball from the feet of a second-row player.
d) When the referee blows the whistle for an infringement.
e) When the ball in a scrum is on or over the goal line.
However, depending on where you are, there may be local changes - in Aus (NSW) my understanding is that local law variations carry through into 7s (i.e. Tackle Height at Sternum and Scrum Half at Tunnel - so here the half needs to stay at the tunnel instead of behind the ball).
EDIT: referenced team in possession, so updated to correct