You are very right! I must have miscalculated when I typed that. I'll edit that post.

For the sake of clarity, the cutoff is T-75, and most airlines are usually pretty strict about this. So, working backwards, I aim to get to the airport at T-90, and I allocate between 30 and 60 minutes for my taxi. This is contingent upon both traffic, and where you're setting out from. For example, even with no traffic, tack on an extra 15 for downtown v CBD. Unfortunately the Airport Express train isn't practical from many locations, especially if your baggage is too bulky to tote on Line 10 (extremely crowded) or Line 2 (not as bad as Line 10, but the odds of getting a seat are still quite low).