Full-time lateral advice

Wait until around late January and then late May of your first year to network and apply. Firms will start posting applications then because of attrition once people leave post-bonus in February and July for winter-cycle employees and summer-cycle employees respectively. You also don't want to give the impression of hating your group by starting to network now before you even started.

Speaking from experience, wait until your first year is up to lateral. I got way more traction after waiting for my first year to have finished in May/June. By that time, you'll have closed deals to put on your resume, be able to speak about your knowledge on X industry, and be able to speak on your strengths/weaknesses/ranking within your group at a more mature level, which is what they want in an experienced lateral analyst. That said, the market for lateraling is really great right now since deal activity is at a high. So would be worth it to take a shot after 6 months in Jan next year.

Coming from a top BB (GS/JPM/MS) in a regional office in a top group, I actually didn't have to network to get interviews. It might be different if you're coming from a MM, but I would say if you have high-profile closed deals on your resume it's clear to HR that you are a top performer and you'll get pushed to an interview, especially if you're going to the same coverage group (such as industrials to industrials). 

Also, British headhunters like Pearse Partners, Blacklock, and Maxwell Bond cover a lot of U.S. lateral IB roles for some reason, not just London IB roles. SG Partners, Madison Hunt, and Weatherly Group in the US cover some lateral IB roles.