You could put in a timing relay, wired to latch upon the first signal from the photocell. Set the time so that the solenoid will operate long enough to achieve the desired opeation. When the time runs out, timer de-energizes itself & the solenoid.
I use a similar timer for a diesal fuel pump that the truckers just can't seem to turn off. I think it cost around $40 or $50, has selectable time ranges from seconds to minutes to hours.
Maybe someone else has a more elegant solution.
