They used to go to weekends only in winter, but since January 2018, they've heavily promoted their "365 days of thrills", even with the post-COVID reopening. But their hours are much more limited in the off-season/weekdays -- typically 10:30-6 pm weekends and 10:30-5 on weekdays in winter (my impression is that they try to cover all of the work with a single 8-hour shift of employees).
https://www.sixflags.com/magicmountain/plan-your-visit/park-hours