Often the length of time it takes to complete the form depends upon how well developed your thinking about the project itself is. If you have a fully developed project proposal completing the form may only take a few hours, but if you have not thought through all the ethical issues about your project it may take a few days to complete the form and all other paperwork.
Once you have completed the form, you need to obtain the Head of Department signature which you need to organise with your Department Secretary.
If the project is within the remit of the UEC the form should reach the UEC manager on or before the deadline date (all dates are advertised on the UEC website). The UEC manager will usually contact you within a few days of the UEC meeting. Often a few amendments are necessary which can be approved by the Chair of the UEC in between UEC meetings, and usually within a few days of the amendment being sent to the UEC manager.
Arrangements for the Departmental Ethics Committee (DEC) vary between Departments and you should ask your Department Secretary for advice about your local DEC.