If you are running the Mish thermostat[or equivalent] it is a pretty safe bet that as soon as you are up to normal operating water temp, you are good to go on the cam, from my experience. I put gauges in because I was doing research, and I love gauges. If you had one, an oil pressure is the one to go with. You can infer the oil temp from the oil pressure. Make note of your, say 4k rpm oil pressure when full hot. It will be lower than when it is dead cold or even medium warm. You then can judge what temp range your oil is in.
I would check that my oil coolers stay cold when the car is cold, and get hot when the car is hot, when I think of it, if I wasn't running gauges