It is an all day affair starting around 0830 finishing about 1800.
You will be told on the day if you are going further, If the answer is yes you will do a sim the next day.
Day starts with a psycometric test, formal introductions to other candidates. Then a technical exam followed by a group exercise, break for lunch. In the afternoon there is a lot of sitting around waiting for your ability test (card game spot the missing links) and interview. The only part you can prepare for is the technical test. See the Cathay interview book for some sample questions. Think they have a new paper in the works but the Cathay book will no doubt still point you in the right direction. Have a good look at the Easyjet web site, it gives you a feel for what they are looking for.
Interview is fairly standard brush up on swept wing theory, met & notam decodes. Few HR type questions, like descride a difficult situation and how did you deal with it? what was the outcome?
Hope this helps! A busy day but very friendly, good luck!