Wood – How hard should water based polyurethane get

What you will want to do is to get a polyurethane stripper with brush, a pair of rubber gloves, a scraping tool, fine grit sandpaper (200), a clean cloth, and a well ventilated room.

Start by applying the polyurethane stripper liberally and evenly over the wood using the brush. Let it stand for about 5 minutes or whatever the directions instruct you to do.

Using the scraping tool, gently scrape off the polyurethane in the direction of the wood grain, taking care to remove the scrapings as you go along using a clean cloth.

Once the scraping is completed, lightly sand the wood in the direction of the grains until the surface is smooth.

You're now ready to apply the finish of your choice, whether it be polyurethane, a stain, or paint. :)

It's possible it's just the cool temperature and it will dry in a few days. It won't hurt to let it sit several more days and see if the tacky areas harden up on their own.

However my suspicion would be a compatibility problem between the urethane finish and the "green" mineral spirits. Although they probably say then can be substituted for real mineral spirits, I've heard of mixed results when using them for thinning oil based finishes. For a future project you could select all water-based finishing products which would have lower VOCs and would not require thinning with any solvents. Or use standard mineral spirits for thinning and save the "green" ones for cleanup.

If the finish doesn't harden on its own I would try to remove most of the finish from the tacky areas as you described. I would do it in stages with some drying time inbetween because if you remove too much you will likely also remove some of the stain resulting in inconsistent shading. In that case you may need to strip and refinish a larger area (or live with the spots).