Geez, I must not understand.
My oven has a delay start mode (you could set for before Sabbath) and a timed delay shut-off, after so many set hours.
If you want to be in compliance with your rules, you can look at the panel lights to tell if the oven is still on, or look at your watch to see if its "safe" to open the door.
possibly. there is no prohibition (in a conventional oven w/o sabbath mode) to setting the heat all the way up 500 or more the 30 minutes before sabbath, turning the oven off right before sabbath (18 minutes before sundown),placing your dinner in the oven and expecting the residual heat to keep the food warm for a couple of hours until when you are ready to sit down. IMO theoretically, (only) having the oven click on during sabbath is ok provided you are not cooking (warming only) and the food is already hot. that is, you cannot cook on sabbath regardless of the oven settings, timers, etc. this is a separate issue from the electricity and has been discussed earlier in the thread. the food must be at or above the temperature the oven would be set at and not benefit in any way from the new heat (improving the food). a possible example would be from the blech on the stove directly to the oven. this is still problematic and i am not recommending this to anyone for whom it applies. it is theoretical only and should be discussed with the LOR if necessary to implement. i am not a Posken.