I was told it’s fine to have a hot plate turn on and off on a clock. The only issue would be if you want a hot/warm liquid item Shabbos morning. Liquid can’t be rewarmed, so it would need a continuous source of heat from before Shabbos starts.
I have my hotplate turn off at about 11:00 Friday night, then turn back on at about 8:30 Shabbos morning. I put two pans upside down on the top, and put my food on top of them before leaving to shul. Then, when I get home, the food is nice and warm for our meal.