While doing Drupal development, you sometimes might want to find out how fast or slow a certain part in your code is. Did you know that Drupal has 3 easy functions to do this built right in to core,
You can have multiple timers in one run and each one of them is identified by the
$name parameter you have to pass to each of these three functions.
I think the functions are pretty self explanatory:
timer_startstarts a timer
timer_readtells you how long the timer has been running
timer_stopstops the timer and returns an array that contains the number of times the timer has been started and stopped (count) and the accumulated timer value in ms (time).
Source: http://www.drupalcoder.com/story/336-how-to-measure-the-execution-time-o... (Drupal 5.x)