I'm not in the situation of having 2 exams in one day, and i sympathise with people who have shocking exam timetables.
But i honestly think that by the time the actual HSC rolls around, what real good is an extra day or couple of days going to do? Basically zilch. By that point, cramming or trying to learn anything new seems pretty pointless, and not of great help.
A bigger gap would probably be nice - just for peace of mind, but really, the difference is negligible in terms of actual "advantage" HSC exam-wise.
So for those of you who have consequtive exams, or 2 exams in one day, (or worse!) it is a bummer and does seem scary - but on the bright side, it will in all likelihood NOT affect your performance, and it's probably good to get things just over and done with.
anyway, good luck and don't stress! I'm sure you'll do well regardless of what the timetable throws at you.