Define "VIP"? Just a VIP as in "as_"-maps (the guy with 200 hp and pistol only) or someone with special abilities/options?
You could use the stats system if the player is logged in via U.S.G.N. - otherwise you have to count the play-time yourself. E.g. by using the second hook.
This is how you can ceck if the player with the ID usgnid has been on the server for longer than one hour (60 * 60 seconds = 60 minutes = 1 hour)
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if stats(usgnid, "exists") then
	if (stats(usgnid, "secs") >= (60*60)) then
		-- do your VIP stuff
	end
end