We met and solved this problem. The root cause is that, as default, mrbs monthly updates timezone information via Internet. If your mrbs installation is behind company firewalls, timeout occurs while editing / adding new booking entry in 28 days after a whole new mrbs installation.
The easiest solution is to disable the periodical timezone update (if your installation does not require daylight saving ...) by adding a specific option in your config.inc.php:
$zoneinfo_update = FALSE;
If timezone info is concerned for you, it's probally necessary to consult your firewall administrator to allow mrbs access to Internet. For more details, please check mrbs documents, like systemdefaults.inc.php:
35 // If you are using iCalendar notifications of bookings (see the mail settings below)
36 // then the iCalendar attachment includes a definition of your timezone in
37 // VTIMEZONE format. This defines the timezone, including the rules for Daylight
38 // Saving Time transitions. This information is included in the MRBS distribution.
39 // However, as governments can change the rules periodically, MRBS will check from
40 // time to time to see if there is a later version available on the web. If your
41 // site prevents external access to the web, this check will time out. However
42 // you can avoid the timeout and stop MRBS checking for up to date versions by
43 // setting $zoneinfo_update = FALSE;
