I had a problem due to php memory that was crashing my site

Hi,
I had a problem due to php memory that was crashing my site with the appointments plugin. I fixed that and reloaded the plugin. Everything seemed to be fine and now suddenly 1 week later, when I try to view the page to make an appointment I am getting this error: Fatal error: Maximum execution time of 30 seconds exceeded in /home/jupiterlily/eventsatjupiterhotel.com/wp-content/plugins/appointments/appointments.php on line 3900

My site is http://www.eventsatjupiterhotel.com.

Thanks for your help.
Zoe