Of course we can
Friday 19th October- set up, register, welcome and icebreaker social
Saturday 20th October & Sunday 21st October - workshops, hangout social zone, stallholders, geocoin area, games and competitions, ancillary event caches,
Monday 22nd September - CITO, tear down, depart
The main events will be Saturday/Sunday, but there will be some on Friday evening, as well as Monday morning (CITO). Hence if you want to be involved in everything, the best plan is to arrive Friday afternoon, and depart sometime after lunch on Monday. Of course, there may be some additional ancillary event caches that pop up around the MEGA as well. The 3-day bit broadly covers the Friday evening through to Monday lunchtime.
A subgroup of the MEGA organising committee is meeting tonight to work through the first batch of FAQs - I'll add this one to the list so we produce a more formal answer