WR changed the wording of the law on this, way back in 2018.
It used to be worded in line with the traditonal English way of managing things -- opponents must given reasonable time
old law
19.8(c) The opposing team may have fewer lineout players but they must not have more.
19.8(e) If the team throwing in the ball put fewer than the usual number of players in the lineout , their opponents must be given a reasonable time to move enough players out of the lineout to satisfy this Law.
Sanction: Free Kick on the 15-metre line
it's now worded in line with the rest of the world -- nothing at all about giving any time/warning... (i assume the objective was to speed things up a bit)
[LAWS]18.14 Unless the throw is taken as soon as the lineout is formed, the non-throwing team may not have more players (but may have fewer players) in the lineout than the throwing team. Sanction: Free-kick.[/LAWS]
After the change, I adapted the way I ref this, but in general i reckon very little impact was made .
I suspect many refs in England still have the old wording in their minds somehow.