Well, Mexican Independence is coming up, so BTB's normal deal on the 5th of the month gets extended.
As I hear it, the festivities will be starting at 3pm, instead of 5pm, $.50 shots of Cuervo and $1 bottles to start. Given that school will be out and significant number of the students who stay in town over the summer are the ones who go out to the bar, this event will again be packed.
If you plan on sitting down, I would show up around 2pm. If you plan on getting a seat at the bar (recommended) I'd show up before 1:30.