Because the question is asking about time zones, knowledge of eastern and mountain daylight time zones is needed. (But don't worry, a quick Google search will reveal the distance to you - or even in the clock app of your iPhone!)
If the time in Colorado is 10:00pm, the time in New York would be midnight, so the latest you'll hear from them is before midnight in your time zone! (where it is still technically your birthday for you!)
Hope I helped!! :)