Hi Richard
I usually recommend keeping a day diary for a week, if you have a flucturating condition then you may want to extend the period.
I cannot answer your second question, all I can say is that I have never had any issues with a claimant completing a day diary, infact the opposite, as it can be quite useful for a decision maker to help make their decision and tribunals also find them useful.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
