Burner Standard Time is the approximation of the time a meeting or event will take place between two attendees of Burning Man, which takes into account the reality that Burners are easily distracted and often late (especially at Burning Man). For instance, 4pm burner standard time should be understood as anywhere between 4:30 and 6pm "real" time.
While it is common parlance at Burning Man, it has application outside of the festival as well.
At Burning Man:
"Let's meet by the temple at at 3 o'clock burner standard time"
Outside of Burning Man:
"Larry is late again!" "Oh, he's still running on burner standard time"