One of Lian's most frustrating idiosyncrasies is his inability to recognize the passage of time. Five minutes or five hours will stretch eternally for him. We discovered pretty early on that time outs would induce a melt down that eclipsed whatever infraction warranted the punishment. He just couldn't see the end of if it and it terrified him. Timed tests are impossible. He is caught between the possibility that the time will last forever and the fear that it will end at any moment. That kind of uncertainty doesn't make for optimum testing conditions.
Over the years we have had great success with the use of alarms. A bell signals the beginning and end of school, playtime or the end of an impatient wait. For some situations we a standard kitchen timer, however a visual timer is what works best for him. Something he can look at and see how much time is left. We have looked for years to find a good visual timer to buy. There are some nice ones out there (ex. http://www.difflearn.com/category/timers_counters_clocks), though they can get pricey.
With as much time as we spend on the computer, it makes sense to have a timer on the computer. A couple of computers ago I had a great desktop gadget to help us out. Sadly most of these great gadgets have been eliminated and our timer went bye bye. This week, I was excited to find, on Pinterest, a great website for online classroom timers. http://www.online-stopwatch.com/classroom-timers/
Not only does it offer several fun options for a timer that will appeal to any classroom situation. There are also many other timer tools available including stop watches and even a metronome. Already in the few days we have been using the timers on this site, life is so much easier for the boy, or at least a little more fun. He prefers any of the timers that explode. My favorite is the simple hour glass.