You are apparently “self connecting”, i.e. planning two flights which are booked separately, with different airlines, so you are right to be cautious, as if for any reason you miss the check-in deadline for the second flight, you’ll be considered a no-show, and in most cases the airline operating that flight will just cancel your ticket (including any subsequent flights on the same ticket, but I believe this is not an issue here), and you would be on the hook to book and pay for a new ticket. (Some fares would protect you from this).
The rule of thumb is to have at least 4 hours between two such flights, but the longer the better.
In your case, you have 11 hours, which is a lot of margin. Add to that that there are quite a few other flights (just in case the flight is cancelled altogether or very severely delayed for a reason specific to that flight).
You can use tools such as FlightAware to view the recent history of the same flight (or actually another flight at roughly the same time, I can’t find an exact match, probably due to planned schedule changes). Over the last two weeks, the largest delay was still under 2 hours, with most flights being less than 30 minutes late.
The only big issue I would see (depending on when you will be travelling) would be large-scale weather disruption in Seattle. You may want to make sure you have travel insurance which would actually cover rebooking of the second flight in that specific case.