Hi SomedayMaybe,
Although I haven't undertaken any of the ATPL exams yet, I have my first seven later this year, in November. However I'll try to answer your questions.
1) The JAR-FCL ATPL Exams are in the multiple choice format.
2) Varying amount of time available depending on the paper (anything from 30 minutes (both VFR and IFR Comms) to 3 hours (Flight Planning) duration).
3) Varying number of questions per paper.
4) Pass mark is 75% per paper.
The timetable for the exams is available in Lasors, but in short is three to four exams per day over a period of four days within the first full week of every month. The course that I am on has planned its modules in order that we only have no more than two exams per day.
http://www.caa.co.uk/docs/33/LASORS.PDF - Section J.
On a slightly different subject, I see you are from Cardiff. Do you fly already and if so from Cardiff? I probably know you if you do...
Best wishes,
Charlie Zulu.
PS. Welcome to PPRUNE.