I always try to choose tasks that bring the engine up to proper oil operating temp ( 190F on a guage). That is not always easy for a homeowner (vs pro). Drives the accumulated moisture out of the oil, and promotes proper lubrication. If you perform lots of short tasks I would dump the oil based on time (often).
wjj, As stated above the oils are very good at holding moisture without corrosion up to a point. If you are using synthetic perhaps it is ok to extend the drain interval, but i believe that still asumes full operating temp is reached. Each time the engine is used and stopped cold, moisture is there, and each additional cold usage adds moisture. Of course , at 290F you get other problems ( like head disassembly).