Your insticnts are perfect. No reason to wait - actually its better not to.
Once you rop the pn and change the filter (and reassemble) you can fill the trans case with fluid, detach the return line and watch for bubbles or clean fluid. If you get bubbles first, turn off the car, put more trans fluid in and run again. This will flush it all. Once you get clean fluid you can stop and put the line back on.
Do not worry about switching through the gears until after your flush is done, you have refilled to the proper level, and now want to shift through reverse and drive to get any of the last bubbles out.
Check your level again, top up if needed, go for a drive (10 min) and recheck level again. Follow your instincts/thinking - you are on the right path.