If you are using artist oils, it could take several days or so for your wash to dry, depending on how much thinner you used. Personally, I don't seal my base coats prior to washing. I put washes over straight enamel base coats. Interestingly, the wash tends to "bleed" slightly around the edges of what I just washed. In many cases I like the effect, since oils and greases tend to leave larger stains than just in a crack or crevice. But then these are armor models I'm talking about. For aircraft, a sealer is almost mandatory, I think.
Gip Winecoff