If you've never been grunion running then it is time (March - August)...
Yes, you may make the trip and not get to see them but it's always fun being on the beach anyways...
Go to this page for the calendar and more info...
http://www.dfg.ca.gov/marine/gruschd.aspNote: The times given for each date reflect the probable two-hour interval during which a spawning run may occur. The second hour is usually better. The best runs normally occur on the second and third nights of the four-night period.