Actually, trying it again a couple of times, it fails on a different file each time. This confirms that it is no particular code that is causing the problem, but that time is exceeded at various places depending on the load each time. So only what can be expected with a 30 sec limit.
Here is a sample of the error:
Fatal error: Maximum execution time of 30 seconds exceeded in /home/your domain/library/WT/Date.php on line 276