Bill Tindall, E.Tn.
As a result of doing what you what to do with dozens of air dried drawer side pieces.........Do this: cut to rough length, resaw, make stacks of the resawed pieces with thin stickers in between and clamps on the corners to hold the sandwich together and flat. Then put the sandwiches somewhere to dry. (just completed using 18 pieces for drawer sides processed this way. )Many dozen preceded these, more of less successfully, until I found what was necessary.

Humidity inside is likely low now and will be suitable. Marvel at how much you have to tighten the clamps to keep the sandwich tightly squooze together as the pieces dry and shrink. When the sandwich is no longer shrinking, about 1-2 weeks, then proceed to flatten one side and plane to thickness. I do 7/16 sides with slips, but if I did not do slips I would do 1/2".

If you short cut this suggestion you risk warped sides as the thin pieces dry to current indoor humidity from whatever the moisture content the lumber is now.