In my 1L year firm networking events started the day after the ABA-mandated date where firms can start talking to students (Nov 1st? I don't remember for sure), then was in full-swing by winter/spring semester. Before students left for the summer they'd pretty much figured out which firms etc they were interested in. Big firms higher earlier than most other legal employers (as far as I'm aware). Sometime during the summer bids were submitted for the OCI program then during September we actually did OCI (though now its in August I think). As far as I'm aware there isn't a set time table for non-biglaw jobs, though most will be later in the fall semester or very early in the spring semester. Check with the specific entities that interest you. Judges typically start shopping for interns late the in the fall semester or over winter break.