Diving Edmonds at a zero tide is something I would not recommend! It makes for a VERY long walk out along the jetty (or worse, a long shallow wade). On the other hand, if you prefer wading to surface swimming . . .
Saturday morning is a moderately large exchange, so there will likely be some current, but at least in my experience, currents at Edmonds are only rarely very strong. I don't have my book with me that has all the current corrections, so I can't tell you what it would say about the best time to dive there, but for myself, I'd get in the water about any time before noon. It's a big ebb, so if there is current, it should be northbound, which is better because it won't take you toward the ferry. If you get blown north, the worst is a long walk in gear back to the parking lot.
I've never been able to correlate the viz there with the tides, although it does tend to be worse on big exchanges, because the water is so shallow and the bottom is silty. It's also worse when the surface is disturbed (i.e. when it's windy).
The key to coping with currents there is to drop just about at the end of the jetty and head out at about 300 degrees. That will bring you to the rope which is Jetty Way. Swimming along that rope will give you some very good information on the strength and direction of the current, and you can use that for the rest of the dive as navigational correction.
Have fun! There's always stuff to see at Edmonds.
