Most domed crystals on Timexes are acrylic and are easily polished. There are several methods favored by various members which you can find by searching the forum for terms like "buff", "polish", "grit", "emory", etc. The method described below is just one of the many effective techniques used by our members, so check them all out and decide which is right for you.
I usually remove the crystal and use wetted wet N dry sandpaper. For heavy scratches, I start with a 600 grit. Progress to 1000, 1500, then 2000. This leaves a smooth but foggy finish. I buff with a cotton buffing wheel and Tripoli and then buff with a clean buffing wheel. Takes about 5 minutes, but with a little practice, even heavily weathered crystals come out like new.
Since I usually remove the crystals, I fashioned a tool to facilitate the work. I made the gizmo shown below out of a 1 in. diameter suction cup used to hold window ornaments (works with most men's sized watches). I drilled a hole through the middle, inserted a 4d box nail for an arbor, and covered the head of the nail with an adhesive felt pad to prevent damage to the inside of the crystal. I mount the crystal (wet) on the holding device, and place it in my cordless drill. I hold the paper in my fingers. I prefer this method because it results in near factory surface evenness and makes it easier to polish the curved contours near the edge.
The graduated sandpaper method can also be used on an installed crystal by placing the sandpaper on a flat, slightly cushioned surface and moving the watch case, crystal down in a random circular motion. Since I finish the polishing process with a cotton wheel treated with Triploi compound, I will often mask the bezel with tape to prevent inadvertent abrasion to the case.