Converting events in an agenda to textual format
This is very hard to read. What's an internal, why are we converting to it? What's an agenda? This is clearly a class method so I'm missing some context but it's not a self explanatory function. You could improve this with proper naming. x and t are meaningless. For instance, if x was appointment_times it would tell me much more.

Likewise, your code is not broken up at all. It's one solid block, which makes it harder to see what each individual section does or even is. Adding whitespace will make it much clearer immediately:

def convert_to_internal(self, agenda):                                          
    x = []                                                                      
    t = OrderedDict(sorted(agenda['timconf'].items(),                           
                           key=TimeSerializer.__day_comparator))                

   for day, items in t.items():                                                
        day_num = TimeSerializer.DAYS_INVERSE[day]

        for item in sorted(items, key=lambda k: k['begin']):                    
            for attr in ['begin', 'end']:                                       
                if hasattr('item', attr):                                       
                    item[attr] = item[attr] + day_num*24*60*60                                   

            x.append(TimeItem(**item))                                          

    p = ';'.join(map(str, x))                                                   
    return "-t {} -n {} -p '{}'".format(agenda['timeZone'], agenda['locale'], p)