Depends a lot on the flight gods; but last time I flew into SEA from YYC I landed in S. Alaska likes to cycle their international planes out of the A/S terminals in my experience. In that case, you're pretty darn close to your destination, and it's a non-issue. If you land in C, it's about 15min either walking to the A/S train cycle and another 15min to get to your gate. I'd call it 30min to get there, 45min if things go very wrong. But, it's very hard to know what gate you'll land at.