How much time should I expect to spend here? Also, I'm headed up to the tulip fields in Skagit, can I do both in one day? Would it be better to visit in the am like 10am or in the evening like 6pm, during the week?

Yes, you can do both in a day....1-2 hours is plenty at the Locks. No particular time, the Garden is in bloom and you might spot a ship or two "Locking Through" ...no Salmon this time of year, so not worth looking in the Fish Ladder for them.

You could easily do both in the same day. 30 no,utes at the locks is ample time then an hour and a half drive North to the tulip festival. Check out their website for a good guide of which farms to hit.

I think you can do both in one day. You can spend as mich time as you like at the Locks.(watch as many boats going through aa you like). And there is a park that you may like to walk around a bit. An hour or so will be good. I think you can do both in one day.

Depending on the weather (if it's nice stay at the locks for a picnic) only about an hour or so, the drive up to the tulips is about an additional hour, possible to do it all in one day but 2 might be best.

Neither cost... both free