AS requires pax to be at the boarding gate no later than T-30. That gives OP 10 minutes from brakes locked on the inbound to the gate reader on the outbound. If the xSEA flight is at risk of an oversale, offloading OP is an easy selection as it avoids IDB/VDB and leaves OP out in the cold waiting for the next flight with availability.
Either take the earlier flight or pop in the night before, have a good time at SEA and have a leisurely start in the AM.