One problem with that is it doesn't really tell you how much of that time is spent in your program and how much is spent by your program waiting (for a database, or the network, or a disk drive, or another program getting a time slice, etc.). There's not much point in trying to speed up a piece of code that does nothing but wait for something out of your control.

If you still like that style of timing anyway, you could get better results with Time::HiRes.