From DT Seattle, I'd allow at least 35-45 minutes on a Sunday to drive. Tour itself I think is about 1- 1 1/2 hrs so allow yourself 2 1/2 hours there. 45-60 mins to drive bac.

What I'd do is find the cheapest net rental DT Seattle returning to SEA. Go priceline yourself a 3* hotel at SEA. Return the car to SEA, take shuttle to the hotel. No hassles/worries about returning next day, or parking fees.