6:00 pm CST might be unsuitable for EST time zone
When planning a call between Central Standard Time and Eastern Standard Time, you need to consider time difference between these time zones. CST is 1 hour behind of EST.
It is 6:00 pm in CST. This does not fall within the span of usual working time between 10:00 am and 6:00 pm in EST, but it still might be suitable to arrange a meeting, since it would be 7:00 pm in EST, which is between 7:00 am and 11:00 pm EST time.