I don't think this is just a Brazilian thing. When I throw parties in the US nobody shows up until 30 mins after the start time, and the peak of people showing up is between 60 and 90 minutes after start time. The exception to this is dinner parties, where people are much more punctual because they know you're planning the meal timeline.
When I'd ask why they were late, it was the same reason each time. "Oh, we were watching a movie." A typical movie is 90 minutes long, so they would've been putting it on just around the time the party started.
In general though, everyone was a good 20-30 minutes late, but a few people and myself would show up early to help the host prepare last minute food/drinks.