Really depends on the casino and the stakes that you are going to be playing at. At the bigger rooms will have multiple 1/2, 1/3 table running so you will get a seat fairly quickly. If you want to play 2/5 or bigger only certain casinos spread those games and there is usually a wait, unless you are playing at Aria, Bellagio, or the Venetian.

@Las Vegas yeah iam in Canada and I was looking at parq casino in Vancouver but it's kinda hard to tell thinking about just going in to see

@Slytheranprince like Jack to Helen, ain't no telling. You have to go in and get to the know the Casino patterns

usually there is a list. a lot of variables(day,time,weekend,holiday,wsop event) on how long it could be to get a seat.

tl;dr : If the room has games going and there's no list: Yes you can play immediately.

@Slytheranprince : We need to unpack your questions a little (bear with me). Things to consider....
1. Is the casino running games at the time your going? Some rooms have games going 24x7, some places close at 1am, 2am, etc. Some places simply can't keep poker games going. This is easy to tell if the room is registered with Poker Atlas, you can just login and check how many games they have going on the app. If the room is on the Bravo App, sometimes it shows up, sometimes it's weird.
2. What is the wait list like: Depending on the day / time, rooms can get busy. If there's a waitlist, you might have to wait 10 minutes to a couple hours. Again, get PokerAtlas on your phone, and if the casino is a PokerAtlas room, you can register (usually 60-90 minutes ahead of time). This will generally put you on top of the list when you arrive

Other Notes: I'd recommend you start with $1/$2 or $1/$3 games before attempting to play $2/$5 or up.