I am not licensed to practice law in Washington, but according to this treatise posted by a Washington attorney a year ago at http://www.avvo.com/legal-guides/ugc/the-proper-steps-to-start-and-eviction, your calculation is correct. The Saturday day of delivery does not count, but the Sunday does.
I agree with the previous poster that weekend days will count towards the 3 days in a 3 day notice. The court has ruled in the past that the 3 days in a 3 day notice are calendar days and not business days. Keep in mind also that the day of service does not count towards those three days. If a person served the notice to the tenant personally on Saturday, Sunday would be day one, Monday would be day two, Tuesday would be day 3 and Wednesday would be the first day a summons and complaint could be served. An important caveat is that if you did not personally serve the tenant, but rather posted the notice on the door and sent a copy through the mail, or served someone other than the tenant and mailed a copy through the mail, you must add an additional day before you may file a summons and complaint. Thus if you served the tenant via these methods you would have to wait until Thursday.
Furthermore, make sure that you served a copy to each tenant entitled to a notice. If there are 2 tenants on the property, even if they are married, you must serve each tenant with the notice. Thus if you had a married couple on the property, and you served a copy of the notice to the husband, you would then also have to serve another copy to the wife by one of the mentioned methods. Below is an example:
You knock on the front door of the house, the husband answers. You serve one copy of the notice to the husband. You then must ask whether the wife is home. If she is not home, you serve another copy to the husband to give to the wife. Now, because you were able to personally serve the husband, but not the wife, you must also mail a copy of the notice to the wife via US Mail. Thus you timeline would have to add an additional day before filing a summons and complaint.
I am not trying to confuse anyone, but these rules must be strictly complied with. A court does not have jurisdiction to hear a case unless the statute was followed to a T. A good attorney for the tenants will always be on the lookout for procedural errors.
If this is your first eviction, I highly suggest that you discuss the matter with a local attorney to make sure that you understand all the rules involved in service of these documents. The rules are strict because the unlawful detainer process is a shortcut create by the legislature to return property back to the landlords. In order to take advantage of this process, you must follow the rules strictly,
Well, with all due respect previous posters are incorrect. Recent caselaw from WA's Supreme Court hold that a 3-day notice is not subject to CR 6 so The three days includes the weekend. Theoretically you could serve a 3-day on the Friday of a 3-day weekend and go file the unlawful detainer on the next court day. I don't recall the party's names but it was out of Div III and Joseph Puckett represented the landlord.