I’m not sure if this is totally correct and I have no fixed way of measuring this (other than that I don’t get any timeout errors anymore) but I’ve noticed a significant difference when choosing between two different methods of string concatenation:

Slow way:

foreach($oranges as $orange){
$orange_str = $orange_str . $orange;
}

Better way:

foreach($oranges as $orange){
$orange_str .= $orange;
}

This is obviously simplified for example’s sake, but I had a situation where I was concatenating several hundred (maybe a thousand) elements to a string and I was receiving a “Fatal error: Maximum execution time of 30 seconds exceeded…”.  My best guess is that with the first method, an actual copy of that string is being made in memory so you’re probably taking up twice the amount of memory than you should be.  That’s just my guess.