As I understand it:
You are exempt for up to an i itial period of 3 hours if the restriction is for a period greater than 3 hours and:
b)a parking disc is displayed in the relevant position on the vehicle marked to show the quarter hour period during which the period of exempted waiting began.
"parking disc” has the meaning given by regulation 8(5);
8(5) In this regulation “parking disc” means a device which–
(a)is 125 millimetres square and coloured blue, if issued on or after 1st April 2000 or orange, if issued before that date;
(b)has been issued by a local authority and has not ceased to be valid; and
(c)is capable of showing the quarter hour period during which a period of waiting has begun.
I'd not go in too hard if the above apply - wait for others- because prima facie your 'parking disc', AKA clock, does not comply.