Regarding your last paragraph Tomek; we've developed functionality for this that we're calling the 'Deadlines' module, combined with advanced Extension management (student online requests, group extensions, global extensions etc). I have submitted it for further feedback from Moodle HQ, and will shortly be opening it to the community at large. If you'd like to have a look at it in some further detail, I have been documenting the development process here: https://moodle.org/mod/forum/discuss.php?d=216784
The code is beginning to mature now and is going through our internal UAT process, the source is on GitHub though I haven't made the URL public as yet.