The opportunity would likely reflect an estimate of how many people are awake at that time, precipitating circumstances, potential witnesses, etc. Where real opportunity comes -- both for commiting a crime and for being witnessed committing that crime is anywhere that people congregate. Late at night people tend to be drunk or high and have impaired judgement, you get a bunch of those folks together and you are far more likely to see a problem than in other places. Of course there are far fewer places that people congregate late at night.
But let's keep in mind where you are hanging out -- music venues, right? That's a bit of a different scene. The focus there is more a) on the music and b) talking with your friends. That's far less a formula for criminal activity. Unless you count drug sales and use. Then the numbers likely kick up.
Also, as you note, people don't screw with you. You are a crime deterrent. So again, you are driving crime stats down.
Statistics are not "tricky" per se -- they are potentially objective values that folks need to apply critical thinking skills to evaluate. So you are right -- every adjustment needs to be questioned.