When in the editor the time of day is associated with the info for a particular scenario. So enter scenario editing mode (Scenario Tools icon) double-click on a scenario token for the scenario you're in (The big white-orange looking token that appears in front of for upon entering to edit a scenario) and on the right-side fly out you can enter in various setting for that route such as time of day (enter in 24 hour clock number though. So, for example, 10:30pm you would put in 22 and 30), weather, and Day / Month / Year, type of Weather conditions, etc...
When done entering your changes, left-click on the scenario-token again (or left-click on some innocuous spot in the area), then F2 to save your changes. Press the Play button in the bottom-right corner and the new settings should take effect. Cheers!
