Display results from specific date and timespan

I have requirement to be able to show results of a given date and a given time span of 24 hours from that date.

If you were to pick 1/1/2016 10:00pm with a time span of 6 hours it would display all results on 1/1/2016 from 4:00pm - 10:00.

Users don't know if the time span goes forward or backwards from the selected date. What is a better way to display this UI?