I am very grateful for the answers!
Of course I would be pleased, if my 1 day-view would make it into the main-version, but I need to simplify and clarify the code first.
An unsolved issue is the language file, because as you can see I'm using another date-format than 'd/n/Y'. I couldn't implement set_locale yet and therefore created a simple $month_array = array (1=> 'Januar', 2=> 'Februrar'....). The question is, how should this be finally implemented for all languages?