Except for Oxford and Cambridge, who tell you on a specific day, and Sheffield, who usually give something of a timeline (although even that is a bit inprecise, and they changed it DS's year and pushed it back weeks, but at least they published they were doing that once they had decided they didn't have enough time) - you just have no clue until they start coming out. And even when they start coming out - Sheffield tend to do it over about a week, places like Bristol tend to offer their top scorers in the interview months before they give out their last offers (so you can get some desperately early offers from there, but only for a real handful). You are "lucky" if you have heard by March, and many have finished interviewing in December. Others are still interviewing in March or April and not giving out offers, even though your interview may have been in November. It is a long, painful, waiting game, so it is worth bracing yourself for it. And Kings in particular have been known not to have the decency of even sending a proper rejection, just having you default to rejection after the deadline for offers expires.
All I can say is, try not to let it stop focus on the A levels, although it can be hard. And some universities tend to send out their offers every evening at - say 6pm, or 8pm, or so, so every day you are waiting all day for the deadline, to find out if maybe, maybe you have been dealt with that evening (and then they skip days, or weeks, and you think maybe they have given out all the offers, before another one trickles out). Your first indication (unless you are one of the very lucky ones) that your particular university has offered is likely to come on TSR, so it is worth stalking the relative threads. (we were very, very lucky, as we got an offer from Nottingham in their very first batch, which I think was late February, and even though we had an agonising week waiting for Sheffield, at least we had the Nottingham offer first, once you have one, it is so, so much more bearable). But most do them in batches, and there is only going to be a very few in every first batch, and it can be day after day after day, month after month.