CIC in theory should schedule the test in the order of transfer in dates (all other things being equal i.e. routine application). There is a test capacity based on room size and availability as well as that of the CJ. So if by bad luck you are number 51 and only 50 people can do the next test say on May 14, 2014 and the following test is May 20, 2014 then no dice and your clearances have to be re-run. Clearances are batch processed but give it say 3 months. What you need to worry about is CSIS clearance (intelligence) since it relies on the Canadian authorities getting information from organizations outside Canada - these ex Canada peeps may be efficient or jut plain disorganized.
Of course this raises the question of how CIC deal with say 50 people all with the same transfer in dates! My impression is that they go for a nationality mix which would disadvantage the applicant whose nationality is the bulk of the test group.