This is when night games almost always started back in the olden days, like before 1980. (Actually they started at 8:00.) Of course, that was back when games often finished in less than two hours, back before MLB mandated two or three minutes between innings for commercials, back before batters found out how advantageous it was to work the count, back before multiple pitching changes, etc, etc, etc. But my assumption in this case was that they are trying to allow for another hour of evening cooling. Edited to add: there are no 8:05 starts in Texas on Saturdays for the rest of the season.