My guess would be to try and follow natural sun cycles.

I would try starting with 12/12 for 4 to 6 weeks spring cycle. Then switch to 18/6 for sumer cycle for 8 weeks. Then back to 12/12 till any fall bearing vegitables are ripe.
AGAIN THIS IS AN EDUCATED GUESS!!
I have never tried it so this my be a starting point you may want to adjust as you go.
The reason for 3 light cycles is different plants bear fruit at different times of the growing season. You will have to keep this in mind when choosing type of plants to place in your grow room.