I need to let end users specify a time range, to be stored and used internally as a starting date/time and ending date/time. The range could be minutes or it could be days.
One way I've seen work very well is using a gantt chart:
http://en.wikipedia.org/wiki/Gantt_chart
You can create a single line chart and then you can scale it across months, days, hours and minutes depending on how wide or zoomed in you make the control. The problem is I don't know of any control out there right now that does just one line, so you may need to create a custom one. You could possibly look for a gantt chart control and just do one task/item.