HI – if you call 511, they have a line for traffic and ferrys. I think it includes wait times. If you keep pressing certain numbers, you will get a live human. They can tell you. Or get on the WA state ferry website. otherwise, I can just tell you what the lines are like for Vashon. Both of those ferries are rush hour, so I would be in line 30 minutes before. Rush hour goes from about the 4 pm ferry to the 7 pm ferry. Fridays are the worst weekdays. When you are in the line, if you are as far back as the first Lincoln Park parking lot that you get to driving south on Fauntleroy – you probably won’t make the next ferry. That is not always true, depending on the size of the boat, but it’s a good general rule.
Good Luck!