Can I purchase a ticket the same day or should I get it days before we arrive in Seattle

Same day okay

I would definitely look at getting the city pass.

Yes, you can. I did it. We arrived at 12h and purchase ticket even with no lineup

You can get same day but if you are going to be there all day or for at least 2 i would look at the city pass. It also includes space needle and some other things are well qorth the money. I am a water guy and i loved the Boat rode that was included.

You can easily buy it on the same day.

You can buy the same day.