Hi Geoff, there is no need to use port 88, Airtime uses a virtual host configuration. For example /etc/apache2/sites-available/airtime-vhost.conf might contain first lines like these:
<VirtualHost *:80> ServerName airtime.example.com
ServerAdmin admin@example.com
DocumentRoot /usr/share/airtime/public
So Apache only responds to requests for the ServerName airtime.example.com on port 80 by serving /usr/share/airtime/public - if you are using similar virtual host configurations for your existing sites, they should not be affected by Airtime.
When using the automated .deb package install, make sure you answer 'No' to the question about disabling the default Apache site if you are using that to point to any production sites. For example, /etc/apache2/sites-available/default or 000-default.