12:00 am ET might be unsuitable for CST time zone
When planning a call between Eastern Time and Central Standard Time, you need to consider time difference between these time zones. ET is 2 hours ahead of CST.
It is 12:00 am in ET. This does not fall within the span of usual working time between 9:00 am and 4:00 pm in CST, but it still might be suitable to arrange a meeting, since it would be 10:00 pm in CST, which is between 7:00 am and 11:00 pm CST time.