Using Pb solder, my tips last a very long time (Hakko FX951, cheap orange Weller station) and replacement is usually due to physical wear rather than loss of coating.

Using Pb-free (rare, because I hate working with the stuff) they seem to deteriorate much faster.

Regardless, the key is to forestall oxidation and physical wear of the tip coating for as long as possible.

What I have found that works for me:
Always use good quality solder; I have had the best results with Kester, Multicore, and AIM (Cardas “quad eutectic” is the absolute best I’ve ever used, but it’s tailored to audio gear, expensive, and severe overkill for a pin). Also make sure the tip stays tinned and shiny at all times, particularly if left hot for prolonged periods (if your soldering station has a “sleep” function like the Hakkos, definitely use it), and tin before powering off. Finally, clean the tip with a sponge moistened with DISTILLED water only (very important, especially if your tap water has high mineral content), and use the abrasive brass wool type cleaners sparingly (only when the tip can’t be tinned adequately after a couple of swipes on a wet sponge).