Hi! From what I remember, during the summer Six Flags Magic Mountain is open everyday, although the time it opens and closes does change. Your best bet would be to keep an eye on this website: Six Flags Magic Mountain
If you go to the events tab, you can see what big events are coming soon and see a calender with the dates and times they are open, just hover over the date your interested in.
^ I believe at WCB Q&A, Tim Burkhart said that the 10:30am openings might be rolled back to a 10:00am gate opening allowing guests as far as the borders of Six Flags Plaza until 10:30am. That it's something being worked on currently.
"Who among you is wise and understanding? Let him show by his good behavior his deeds in the gentleness of wisdom." -- James 3:13