Recently the subject of warming up a car came up. Most modern cars warm up very quickly and the water temp gauge reads "normal" within a couple minutes of starting the engine. Based on cars I've owned that have oil temperature gauges, I have observed that the oil takes significantly longer to reach full operating temperature than the coolant does. Something like 10 minutes at highway speed in the Corvette, and a similar time in the M3. The Miata has a much smaller oil capacity than either of those cars, though, so the oil should get to full temperature a bit sooner.
It's important to get your oil up to full operating temperature fairly often so that condensation and unburned fuel that finds its way past the rings can volatilize out of the oil. So, if your daily commute to work is less than say, 5 miles, go for a longer drive every few days so that the oil can get nice and hot (~200-220+ F) for a while. Your engine will thank you.