On Zabbix 2.0.6 we can not change maintenance period on WEB UI Frontend with PostgreSQL.
But it does not occur with MySQL.

As you understand by seeing attached patch, date('YmdHi', $_REQUEST['timeperiods'][$edit_timeperiodid]['start_date']); creates integer value like 201307191057. But it is larger than the DB acceptable value. As MySQL is fool, it converts to integer maximum value. But PostgreSQL does not and issues error.
Though $_REQUEST['new_timeperiod']['start_date'] is almont meanleas variable, I choose non problem value.

It must be applied to 1.8.16.