For me rusting is a secondary concern, I'm leaning more towards of how long can the string last it's "new string" tone, resonance and sustainability.

For example, I've been using d'addario .010 gauge(that one with the pale orange circle on the box) for 8 year now, my experience shows me that:

1 week: That addictive new strings sound, all sparkly, crisp and full-on sustain.
=>The strings are a dream...

2 weeks: That bright new string sound diminishing a bit, the treble decrease and the tone starts to become warm; sustain is alright but noticeably decrease a bit when play solo a above the 12th fret.
=>The strings somewhat feel natural as it settled on the guitar as oppose to newly installed where you can feel the twang~ness of metallic vibes...

3 weeks: Tone is very warm while brightness is moderate to minimal; sustain audibly decrease but tolerable...
=> The strings overall tonality feels resilient when pluck, like it's run out of steam; the resonance of the string is imbalance, meaning the strings resonate/vibrate more vigorous but the volume is decrease which usually on my guitar - fret buzzing imminent for the 1st, 2nd and 3rd strings..

4 week: Tone is warm but starts to darken, lost of treble and brightness; sustain is about 35% less than new sets of strings.
=>You notice guitar skills decrease (decreased dexterity) a bit because the strings lost that ease to pluck;when you start to pluck fast (almost at shredding speed), the tone lacks commitment meaning it's not as sharp as it use to be hence muddy a bit. When soloing, the string's tone is not as commanding. Fret buzz can be heard on the 1st and 2nd string when play...

5 week: Metallic sound almost diminish completely because the tone is too warm and dark; sustain is disappointingly shorten..
=> Dunno bcoz I change already changed strings at this point.

In my opinion, .009 gauge has shorter longevity than .010 gauge; but it's more brighter, twangier, agile and fun to play...

I use 010. because when you pick super fast, a heavier gauge is more composed under relentless stress. (power chords, heavy & fast strumming, shredding, bending aggressively, etc.)
I miss using .009 though, that lightness and gracious of touch with suits well for Fender Tele...

BTW I change string MAX every4 weeks; OR 3 weeks if playing 15 hours per week

Nice tip!

But after you applied the oil, do you re-wipe the strings with clean cloth/tissue/etc. to remove the oil?
Oily neck can be a hassle...

And the bold quote, are for you real?! I have to change strings every 3 weeks after 12 hours play-time weekly...
Might have to steal a bottle of baby oil from my little nephew

Yup, baby oil is more human friendly than those sewing machine 'Singer' oil or the good ol' WD40