Based on the information given, that is when the test starts. I would be there 15 minutes earlier, just to be safe and not being too late (traffic, or other possible issues)
The quick answer to the first question is: No, the office opens at 8:30. The test starts only after everyone is seated in the test room, the information section in the answer booklet is filled in and the test instructions are provided. We were notified of a test time of 8:27, but the test didn't start until 8:45. By 8:15, the small hallway outside the office was packed with applicants.
To your second question, I would agree with Polara69. If available, the parking in Canada place parkade is most convenient, given that most other locations fill up very quickly AND if you park in a coin-meter spot, you don't want meter anxiety weighing on you while waiting, since they have a 2-hour limit.
If you are among the first few to finish, you will be called up relatively quickly for your interview, but I observed the officers to take their time with each applicant, especially with folks who appeared to have lots of entries in their passport(s).