This webpage should dynamically update while in "Realtime" mode, so there is no need to refresh the page. If you click the "Archive" mode option, a time selector will appear and all presented data should be approximately valid at that time.
Routinely, the IEM is archiving webcam imagery every 5 minutes. During interesting weather, this interval is decreased to every 1 minute. So if you pick a minute (ie 35) divisible by 5, you are most likely to get an archived image.
The arrows on the map represent the direction at which the webcam is pointed. Due to software and hardware issues, these directions can sometimes be off.
More information on the IEM's webcam work can be found here.