We use egg timers fairly often, and this was the first time I was so strict about it. I really wanted the whole fight to feel extremely hectic and hurried. The second reason for using the timer is the fact that despite my best efforts, at the end of the day the encounter still only had a small amount of tactics. The timer helped make those few tactics more interesting because they were rushed to choose them.
While we are on the topic - where did you get the egg timer you use? Pilfered from some old game of Boggle, a cooking store, etc?
How long is the timer you use? Three minutes (std egg timer) or is it some lesser amount? (non-standard are far more difficult to find).
Would you let someone else edit them?
And what time in the cast is the skill challenge?
Amazon has a large selection through third party vendors. Do a search for sand timers.
Here's a combo set of 1, 2 and 3 minute timers
Amazon.com: SANDTIMER COMBO SET OF 3: Office Products

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.