OB I am not concerned here with Law 6, but Law 13.
You have to use both.
It requires that the oppoisition be behind their own 10m line - at a kick off. I would read that as being a restart kick from the centre as well - in the same way, when the law requires the kickers to be behind the ball, at a kick-off; and that the ball must travel 10 from a kick-off I interpret these to apply to a restart kick from the middle as well - though this is not specified in Law.
If you want to treat a restart kick from the middle as a kick off then surely the relevant bits of Law 13 should be treated equally?
We all agree that Law 13 is a mess in distinguishing the two and then failing to follow up on it properly. For sound practical reasons we treat them as the same – EXCEPT in the one respect drawn from Law 6: the referee does not whistle for a restart. We are already therefore treating a restart as different in this respect. Arguments about ignoring the rest of Law 13 are irrelevant because we already make a distinction.
This leaves open the question of when a team can take the restart kick. I'm sure most of us have said "In your own time" or similar.
as a ref I would suggest you simply say "Wait - they need to get behind their 10m Line", or if they beat you to iot Blow the whistle and get the kick
retaken - exactly as the Law requires.
However Davet is arguing that in fact the opponents can delay the restart. There is nothing in law either way on this. Law 13.4 does not say what to do if the opponents are not behind their 10m line simply because it does not matter – the referee will not blow his whistle for the kick-off until both teams are ready. There does not need to be eg a provision for retaking a kick if they are in front of the 10m line.
Here is a possible scenario. With time running out Blue kick a penalty from Red's 22m line to go ahead on the scoreboard. Because it is a penalty, all their players are up there in case the kick goes wrong.
Red, taking my view, grab the ball and rush up the field; quick restart, regather, and score under the posts at the other end.
Meanwhile Blue, sharing Davet's view, jog slowly back to the10m line and argue that the referee MUST allow them time to get there before allowing the restart. They wanted to run down the clock a little without going so far as time wasting.
Basically this is not a matter of what the law says, because it is silent on this issue. I don't like giving the opponents the right to delay the restart.
[NB I am not addressing the mini question here, but the general one. Perhaps we need to shift to a new thread.]