Your target animal will have some bearing on how long you leave a set in. I will often leave an otter set in 21 days, and sometimes a week over that, depending on what is happening.
It also depends on how large an area your target animal will work, and the value of your target animal. Our line is not static, and is usually in motion, but if we are catching coyotes (live market), and seeing fresh sign, we'll stay in an area 3 weeks or so. At the same time we will usually be expanding our line.
I have been known to leave a working set in, after everything else near it has been pulled, and it is out of the way to check that set. Possibly, we will have to re-evalute this technique because of current fuel prices.
There are a lot of variables envolved in the decision to move a set or keep it in. Not the least of which may be if you're doing any ADC work thru the fur season.
Another factor might be how large a boundry of land you are working. Sometimes there may be only a couple of access points to a thousand acres or more. This may mean you are going to be using the same routes through the property. If you are going to pass that set site daily on your rounds thru a large tract of land, why not leave all the sets in until you pull out?