There are 3 options, For the early hours (3 to 5,30, I recommend the old bullring (Arenas de Barcelona), an old bullring converted into a mall with food and beverage zones in the 4th and 5th floors. From there is 25 min. walking to the venue, or by bus. Box office opens at 6.00 PM, and the Estrella bar is beside the box office. There is another bar not far from there in the swimming pools, maybe less crowded than the Estrella's one.
It can be a hot day to be all the time outside.