Off days? That would be Mondays. hey, maybe when ranger Ed's shoulder is healed we can invite him along too?
No "parks" are open for night riding. Basically your options for night riding are the Fullerton Loop and anything in the Cleveland National Forest....in Orange County anyway.
Night rides SHARE Mt. Bike group hosts some scheduled night rides in El Morro Canyon, CCSP. check their web sit for dates and times.