How Early do Disney Buses Start?

[BuzzLightYear3]

Hi....I've seen lots of advice to arrive at the parks early even though there's no longer any EE. I seem to remember the CMs indicating that Disney buses start running 30 min. before parks are scheduled to open, but people are advising that you get to the park 40-60 min. before scheduled opening. Do the buses start running that early? We'll be arriving June 6 if the answer varies by time of the year. Thanks for the help!