9:00 pm CT might be unsuitable for MT time zone
When planning a call between Central Time and Mountain Time, you need to consider time difference between these time zones. CT is 1 hour ahead of MT.
It is 9:00 pm in CT. This does not fall within the span of usual working time between 9:00 am and 5:00 pm in MT, but it still might be suitable to arrange a meeting, since it would be 8:00 pm in MT, which is between 7:00 am and 11:00 pm MT time.