admin can search ongoing sessions within a searching range

for #73359266
Two things:
1. To simplify things, you can show only those session that has either start time or end time within the given time window. Can omit those start before the window and ends after the window.
2. Try to avoid querying once per time zone. You can retrieve sessions for a bigger window (e.g. add a padding of 24 hours to both ends of the time window) in one shot and filter out the unwanted ones in the result set by considering the time zone.