I add note ex. "Call at 19:15" and when 19:15 Android doesn't show it.
If you'd like to set a reminder for a task, the date/time needs to be entered within the date box and not within the note area.
So I did! Todoist shows a note 30 minutes after. Ex. "call at 19:00", I see it at 19:30.
Just to clarify - by "note" you mean "task"? Todoist supports both tasks and notes, although notes can't have reminders.
That said, if you add a task and within the due date field, type in "today at 19:00" (using "call at 19:00" in the task name will not set a time for it), you should have a reminder set up for it automatically to "30 minutes before", that is - "today at 18:30".
If that's not the case, please make sure that Todoist as well as all devices you use it on are set to the correct time zone.
Also, if you set the task to "today at 19:00", is the time of the task actually correct? So when you save it, does it show as due at 19:00 or maybe 20:00?