Apparently, the Diplomat brand of ovens ended production in 2008.
Prior to the end of production, Diplomat was part of the MFI company, with the company's Hygena brand name combined with Diplomat.
I have not yet found a user manual for Diplomat Elite Double oven online.
However, I have found a Hygena Diplomat manual online (free) and the manual has instructions for the clock. The instructions MAY be the same for your oven (I hope.)
The clock instructions are on Page 10: Using Your Electronic Minute Minder.