Start Times of 72hr Arenas vs 48hr Arenas

The 4 72hr Arenas (2*, 3*, 4* Basic, 4* Featured) start at 1200 CST Mon/Thurs.
The 3 48hr Arenas (T1a, T4b, and T4cc) start at 1700 CST on a rotating 72hr schedule.
Why is there a 5 hour offset on their starting times?
The 3 48hr Arenas (T1a, T4b, and T4cc) start at 1700 CST on a rotating 72hr schedule.
Why is there a 5 hour offset on their starting times?
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