[Dridzt]

Originally Posted by Jarod24 Just tested the IsInProvingGround() function and it will only return 1 after the player has talked to the NPC inside the scenario and the timer has finished counting down. local inProvingGround = IsInProvingGround();   --Returns: nil or 1.   --Remarks: Will only return 1 after the countdown timer has finished when the player is inside the proving grounds scenario.

Thanks, as I have noted this is an UI function, not WoW API so if it's used by someone it would be for convenience, no guarantees on how it will work down the road.
Currently it is defined as

function IsInProvingGround()
	if (WorldStateProvingGroundsFrame) then
		return WorldStateProvingGroundsFrame:IsVisible()
	else
		return nil;
	end
end

in WatchFrame.lua
It would be interesting to check what C_Scenario.GetProvingGroundsInfo() and / or GetInstanceInfo() return in proving grounds as that's probably a better way to test for them.