9:00 pm MDT might be unsuitable for ET time zone
When planning a call between Mountain Daylight Time and Eastern Time, you need to consider time difference between these time zones. MDT is 2 hours behind of ET.
It is 9:00 pm in MDT. This does not fall within the span of usual working time between 11:00 am and 6:00 pm in ET, but it still might be suitable to arrange a meeting, since it would be 11:00 pm in ET, which is between 7:00 am and 11:00 pm ET time.