The warm up timer is a function of the display. It indicates that your display has an issue that needs evaluation. I would recommend that you have your local servicing dealer evaluate it or send it to our factory service center. It is most likely something to do with the main SPU board. (Signal Processing Board)
I have the same problem, if I turn off the scanner using the switch on the back of the display, and then turn on the display the count down timer will function, after the warm up period I can turn on the scanner using the display switch at the rear of the unit, at this time I can transmit but I don't get a accurate display, after about 7 min, the unit will then work properly with a very good picture and I can see small buoys, other boats and land on the screen. After this the unit performs flawlessly. Once this occurs I can turn the unit off and turn it back on with out turning off the scanner and the count down works as well as does everything, after the unit has been shut off for a couple of hours then I have to do the whole process all over.