There is no need to accept a 20 minute job, for mainstream (my main business) I accept no jobs under 2k because it's annoying to have a dozen mini jobs if you want to keep customers happy and talk to them on the phone, write mails, offer support after finishing it, and whatever else is required...but IF you accept it, it's YOUR fucking job and you better do it quick.
Noone is forced to accept work, but a deal is a contract and a contract must be fulfilled. Call me old fashioned...