First start, I watch the SmartCraft temp gauge as I idle out until I see the temp drop when the thermostats open at about 132d. It takes a while in cooler water - never timed it, but wouldn't be surprised if it's three or four minutes.

After that during the day, if the temp when I start is 100d+, wait 'til it gets above 120 - if the temp is below that, I wait for the thermostats again.