Running three comfortable kilometers but struggling to stay consistent with changing work shifts

I can run three kilometers at an easy pace without feeling wrecked afterward. The trouble is my work shifts change every week, so any plan that says ‘Tuesday, Thursday, Saturday’ falls apart quickly. I've tried running after late shifts and usually skipped it. I'm considering a rolling goal of three runs in any seven days, with at least a rest day between harder efforts. For other shift workers, what system survived the schedule changes?