Writing the thesis report is part of the research project: you should reserve enough time for this activity. The introduction and materials and methods often can be already written in an early stage. Three weeks before the final date, at least the outline and contents should be ready. A draft version should be handed in to the supervisor, who will make suggestions/comments for the final version. When the final thesis is ready, you will hand in a pdf to your supervisor and the persons evaluating your thesis work. Usually this is done at least one week before the final talk. Also Marjan de Lange needs a pdf for the archive of FPE. Your supervisors might request a paper version of your thesis.