When do you use Hyperstimm Backlash or Architects of Pain?

Can folks just clarify for me please. Architects of Pain and Hyperstimm Backlash are both used "at the start of the battleround" and last "until the end of the battleround". That's two player turns of boost from each stratagem.
But whens the correct time to activate them? Do you need to use it at the start of your opponents turn if they get 1st turn, to comply with "start of the battleround"? Is using it at the start of your own turn too late to be legal if you went 2nd? Thanks

Also, can you use these stratagems multiple times? The start of the battleround would be prior to the first player taking their movement phase. If they aren't activated in a phase as such, are they subject to a once per phase ruling? If not, they don't state single use only like other non-phase strats such as webway portal etc.

1. Yes, if your opoonent got the first turn, then you use them at the start of their turn. You use them at the start of the entire round.
2. Yes, using it in your turn if you went second is too late.
3. No you can't. Before the game is the only time described as being out of phases. There is no space between turns which does not count as a phase, so "Start Of THe Battle Round" would be at the start of a movement phase.
4. All Stratagems are once per phase only.

Thanks squid master that's great

Honestly, this is why I never use those strats. I can never remember them on my opponent's turn :-(