pete_run

This might seem a simple question, but I've noticed this problem on most weather forecast sites, and never found an answer in any of their "helps". The block of times are usually given in 3 hour segments. i.e. 09:00 - 12:00 - 15:00 - 18:00 - 21:00 But does the 12:00 signify the centre of the time period, or the start (so it would show details for 1200 through 1500?