It looks like some client code is trying to access an invalid property 
of the date object. Unfortunately if there is no stack trace in your 
log you will have to find out where this is coming from on your own.

You can try something like this in Date.php directly before line 561:

if (!in_array($name), array('year', 'month', 'mday', 'hour', 'min', 
'sec', 'timezone')) {
     Horde::debug($name);
}

This will output a stack trace to a file name horde_debug.txt in your 
tmp directory.

Hi,

I had the actual Horde Webmail running under Wheezy without any 
issues. Made a fresh install on a minimal jessie System and restored 
the database.

All is running fine except one calendar (the one with the most 
entries) in web GUI. Display mode for Day and Week works fine, but in 
monthly and yearly view I get an endless loading Loop with 100% Apache 
load until the following error occurs in syslog:

PHP Fatal error:  Maximum execution time of 295 seconds exceeded in 
/usr/share/php/Horde/Date.php on line 561

I think it has to do with PHP 5.6... but as there is no further error 
logged (with Settings to info) I have no clue...

All other calendars display without an issue in web GUI. The not 
working calendar mentioned above works fine in other Clients 
(DAV/Active Sync).

Thanks for your help and kind regards,
Mario