Wood – Applying urethane to table: brush or pad

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).

When I use oil based products I use disposable pan liners so cleanup means let it dry-up and throw it away. To clean brushes I use a brush spinner to remove as much material as possible. I swish the brush in a container of mineral spirits and brush a piece of dry cardboard to get out some more of the urethane. Finally I soak the brush for a couple of days in a covered glass jar that has just enough mineral spirits to cover the bristles. After everything is clean I set the mineral spirits filled container in the sun uncovered until it evaporates. I would not dump it on the ground! If you cannot find a way to dispose of it contact your municipal public works dept. Most cities have an annual hazardous waste drop-off.