If you've got scratches on your frets, then you are going to need a bit more than metal polish. Use the metal fretboard protectors and depending on how deep the scratches are and how soft the fret metal is, I'd maybe start with 320 or 400 grit paper and sand the whole fret until the scratches are gone. Then it's just working up through the grits, then moving on to Micromesh all the way up to 12000, before using the metal polish.

How much work is involved depends on the fret material. With stainless steel frets it took me around 90 minutes per fret on most frets to get them smooth after a fret levelling as stainless steel is so hard. I have just done a similar job on a Fender Telecaster and that took far less time, though still about 10 minutes per fret as the steel seemed to be harder than normal. On a PBG ES-1, I did a whole fret level, re-profile and fret polishing in about 90 minutes as the frets were comparatively soft material.

Once you've got any cross-wise scratches out of the frets (running a piece of hard thin wire across them is the best way that I've found to tell as you can feel the wire catching on the scratches rather than sliding), then it doesn't take long to go up the grits - normally just a few strokes with each one is fine.