Skin temperature (also "surface" temperature) will be displayed as soon as you initialise CORE and is updated every 2 seconds.
When you first put CORE on it requires about 2 minutes to calculate your current core temperature (see this link to understand the difference).
As long as you are wearing CORE correctly, the measurement will update every minute with your real-time core body temperature.
If CORE receives invalid data e.g. it is worn incorrectly or not on the body at all, it will take longer before it will deliver a valid core temperature after you start wearing CORE correctly.
A known issue is when CORE is on and recording but not being worn, then it is put on and the temperature is unusually high or low. It may take up to 30 minutes for the temperature deliver correct values. This is because the algorithm is built to adjust at the same rate as the human body adjusts.
This known issue will soon be resolved, the CORE off-body-detection will be established so that core body temperature recording initialises first when the devices is worn.