Hi there FNM (I can't possibly shorten your name to Fatty!) - Most LLCs run a pop in on day 3 or 4 by which stage you are usually in ketosis depending on whether you started on the day of your first session or the day after. Recent tracking of ketosis returns has shown that as long as we don't have bars or water flavourings (which you won't have anyway as a new LLer) we tend to get into ketosis about halfway through day 3.
When I first started, the last solid food I had was at 4pm on Sunday and my first foodback on the Monday morning and felt the rotten mouth and weird headaches on the morning of the Wednesday and by the end of Wednesday night I was in ketosis - but as Mike says it really isn't an exact science and no two people are the same - I ate for england before my first WI so I have a lot of glycogen to dump - some people eat healthily/go on an LL prescribed lowcarb plan in the run up so they get in very quickly but have less dramatic losses (so worry that they aren't in ketosis - which is ironic!) hope that helps!