I got about 5 or six pair I rotate through and I keep stuff rather clean so I do laundry about every 3 to 4 days. Never really with filthy one on.
1-3 Days - Got to keep them clean!
4-7 Days - By the end of the week, probably
7-14 Days - They can keep for a good two weeks
14-30 Days - At some point in the month?
31+ Days - Ha! They don't need laundering!
Wait, you're supposed to wash them!?
I got about 5 or six pair I rotate through and I keep stuff rather clean so I do laundry about every 3 to 4 days. Never really with filthy one on.