Since I live by the ocean in the tropics and I sweat a lot my pistols tend to rust quickly. I've tried frequent oiling but the long term answer was getting the blued parts (usually the slides) refinished in hard-chrome. Now they rust very little.
As for re-lubricating I usually do it every time the pistols are used or about every three months if they are in the safe. Some of the lubricating frequency depends on how fast the lubricant thins out or evaporates. A long time ago I used Breakfree-CLP but one of the house gun's slide wouldn't cycle after the CLP had evaporated off in three months since the last lube was applied. Now I use 90 wt gear oil- it hangs around for a long time, works great and is cheap to buy.
Happy Thanksgiving- oldandslow