You need to get busy if you're going to start a Will contest. I suggest you immediately consult with an estate lawyer and see what they advise. They may be able to file a preliminary opposition and that may then buy some time to bring the entire matter into court with all your proof, etc.
See a local attorney who knows the clerks of the court and/or the Judge so that something can get done today. Don't wait.
If Washington is similar to California, you either need to have petition opposing your stepfather's appointment as executor on file before the hearing OR you need to be present at the hearing and let the judge know that you oppose the appointment. I suggest you quickly find an estate planning or probate attorney who practices in the county where the probate hearing is scheduled and arrange to have him/her be present at that hearing on your behalf.
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.
In Washington state a Will Contest must be filed within 120 days of the opening of the probate. Based on the facts you have set forth, you would likely have grounds to assert the Will is invalid because 1) your mother lacked "testamentary capacity" at the time she executed the Will or 2) the Will was the product of "undue influence" by her husband. Your petition to contest the Will would need to set forth the factual basis fir tiuyr belief that the will is not valid and it must be filed with the court within the 120 days or it is waived.