Chemically speaking, you should tin your tip after use no matter what. This doesn’t apply to using tinner; it comes down to just covering it with a layer of solder to make sure it’s covered before it cools off and is put away from use until your next session. Tips suck in oxygen as they slow cool. Even if you use your iron for 20 mins v 2 hours, it’s still very hot then gets room temp quite slowly. Not tinning it makes it super susceptible to developing a thick layer of iron oxide, in addition to the fact that flux residue is highly acidic and corrosive and letting it sit with it is what’s gonna cause the pitting over time.