See post #12. It's still the law.
But it does say 'if the assessment/treatment is completed quickly' - so I'm guessing that's the discretionary element.
So, if an opponent assaults you, but you're not too badly injured, you can play on quickly - but if the assault is so bad you need lengthy...
https://www.theifab.com/laws/latest/the-referee/#:~:text=The%20player%20can%20stay%20on,leave%20the%20field%20of%20play.
In fact, he doesn't even have to leave the field in the first place.
Right - I didn't know about the 30-second thing until fairly recently. So, when it was mentioned I looked it up.
Players have to go off the field after treatment. They cannot come back on for 30 seconds (or longer if the ref forgets they were off the pitch, like Dunk at Spurs).
But I thought...