whats the commencement notice for????
a one off dwelling??? if so, just send it in anyway...
the commencement notice is to alert the building control section of the LA of the commencement of work... to be honest most LAs are so under-maned that they cannot visit every site at every stage of construction....
i would just send it in straight away, saying you commenced 2 weeks ago...
EDIT: i just noticed its for a material change of use, sorry.....
even so, they will not be able to know exactly when you started work, so the same applies....