Does the city pass for visiting multiple centers, could be done in different days or has to be completed in one day (I doubt)?

The Seattle city pass for 5 attractions is valid for multiple days.

My friend bought a pass and yes can be used on multiple days. You do have a 9 day period to use the passes. Still pretty good for $99. Hope this helps!

If you plan to visit the needle and at least two of any of the others it's a better deal than paying individually