Doesn't test invitation mean that your file has met the Citizenship requirement? I don't understand what is the hold up after test completion. What else is there to check, smell and taste the paper application to confirm if its edible?
I don't think you will get an interview then. Chances are that it will be DM and oath directly. As per my understanding, interviews are scheduled mostly within 2 weeks of test section update online.
Same situation as you but I don't think time you take the test has anything to do with processing speed. Processing has its own pace depending on the office and officer and It will be just be another wait, hopefully not very long!