When I worked at the airport, I was also the field rep for Interspace Airport advertising, which handles all of the many displays and advertising things around the building. I represented somewhat of a conflict of interest because if something needed to be put up, or repaired, it would need to be done immediately. I told my boss that that presented a conflict of interest as I would not work for Interspace while on city time.
The solution would be to either wait until after quitting time to do the work, or make some other arrangement. We finally decided to track how long it takes me to fix something and to work extra time in order to balance things out.
The biggest reasons for wanting an airport employee to do the contract work was because they would not have to pay the expense of another security background check, badging an outsider, and familiarity with the airport layout.. It worked out fairly well most of the time. Well, except when one of the mini bosses was trying to prove that they were valuable for something and trying to tell the big boss I was doing work on city time... Which I did, but made up for in free overtime. That, of course, went unnoticed because, by that time, mini boss was already gone for the day.
It can be done, but firm stipulations have to be made and understood so that contract work does not interfere with dedicate time for working for the city.
We have met the enemy and he is us... POGO