Heres what it says on the celebrity website FAQ:
"When calculating which days you can take your test, be aware that the day you set sail is not counted as one of the days, unless the country of embarkation stipulates that the test be taken within 24 hours of arrival."
That's great to know they're available 24/7. I think we have a 30 minute layover at one point
lastly, yes, the above plan means we'd fly into SEA the day of the cruise. It's only a 2 hr flight and there are multiple. But yes I get it. More risky.
It's also a 12 hr drive. Not something I'd like to do.