Its about application methods ... If you are using a brush, it should be new and high quality. The best way to get a smooth finish is spraying, so you are already behind if you are brushing.
Do you heat your poly? On furniture, I bring a pot of water to a near boil, hen remove it from the heat. I barely crack open a can of poly and place it in the pot to warm before starting. Not sure about the temperature, but after a couple of minutes, I remove the can and start applying to the flat surfaces. Be careful not to over load it because it will be runny. Smooth, light brush strokes needed going the length of the piece. Don't "tickle" the work because it will leave marks. When the poly starts to cool in the can, replace the lid slightly and re-warm it.
Let that surface dry overnight or two days. Lightly touch sand with 600+ sandpaper. Blow the surface with compressed air. Wipe surface with tack cloth to remove all dust.
Repeat next coat. Now, turn the piece on its side and do the same with the same process. Then do the other side.
I did a bedroom set for my first daughter this way. She is grown up with little kids of her own now ... and still has the set in storage for her daughter (just born). It remains glassy and smooth.
If that doesn't wind your clock, try this approach using automotive finishes for the ultimate look: