Make sure there is no ambiguity about the deadline for submission and the penalties for missing it.
Another danger point comes at submission time. Be clear about the conditions under which an extension might be granted and how this might be authorised. In addition, be clear about the conditions in which an extension will not be granted. For example, you might want to be explicit that extensions will not be granted for frivolous reasons or because ‘my computer crashed’. There are good reasons for being strict about this. One of the skills that students derive from producing a dissertation is project management. Meeting deadlines will give students the opportunity to practise time management. A student who does not understand the need to keep back-up copies of files will have a rude awakening in the world of work. Furthermore, a student granted an extension is likely to find that there are knock-on effects in terms of exam preparation.