Is it realistic to do the Royal Palace first thing(10:00am) in the morning and San Lorenzo de El Escorial in the afternoon on the same day on a Sunday in November?
I think you would be very rushed. I have visited the Palace several times and each time was well worth staying and seeing something else. Also, they are not 'neighbors' but at least one hour apart by the time you get to the metro, on out to Charmartin, take the train to Escorial, or take the bus....would definitely enjoy seeing them but on both days with time to comprehend some of the details and not just see the blur.
At either El Escorial or the Royal Palace, an optional guided tour takes about 1.5 hours, but you easily could spend more time at your own pace. Buses to El Escorial leave from the bus station under Madrid Moncloa metro station and take about an hour each way, with fewer departures on Sundays (see schedules at http://www.ctm-madrid.es/pdf/661.pdf and http://www.ctm-madrid.es/pdf/664.pdf). As you probably know, Rick suggests that you can visit El Escorial and the nearby Valley of the Fallen in less than a day, but both are closed on Mondays.
It would be a tight fit on most days, and in November when you lose sunlight early, I'd say no. Plus you need to eat at some point. And it will take more than an hour to get to Escorial on a Sunday as the buses don't run as often and it's a 45 minute bus ride alone (don't take the train).
One option is to do Escorial first, arriving before the doors open at 10:00. If you finish and get back into Madrid in time and have the energy, you could then do the palace.