Here is your parts breakdown
Model ED25DQXDW04

Here is the wiring diagram
https://www.servicematters.com/d...0Sheet%20-%202176787.pdf

"Turn knob to off and back to on and again it runs fine for several hours"
When you turn it off, do you have to wait for some time before turning it on, re: to let the compressor cool down?

"but does just turning fridge off and on recyle timer?"
No if you have a mechanical timer, turning it off/on will not reset the timer.
I would check the defrost timer to ensure it is the mechanical type. Item 6 in the "Control" section, just because the tech sheet does seem to indicate some units have electronic defrost control. If in a defrost cycle the compressor and it's fan will be off also the fan in the freezer will be off.

If it is just the compressor that stops, fan still runs, then check the start relay, overload and perhaps the capacitor

Here is a site that may help you troubleshoot
http://www.applianceaid.com/refrigerator.html

I just have to turn knob to off and immediately back on. I think its a mechanical timer because it looks like there is a place to advance it with a screwdriver, under edge of fridge frame.
This all started a few days ago when my wife found everything in freezer totally melted and turning to colder it wouldn't kick on.
The freezer side is now empty and for the last 24 hrs seems to be running ok except ice cubes stuck together but not really melted.
Is it possible to have intermitent problem with timer or thermostat?
I guess now I'm leaning toward thermostat, which looks more complicated than timer.