I allow a warm up time of about 20 minutes. Them it seems to be stable without any further tuning. AFAIK, the tuning stores some coefficients along with the measured temperature. That said, it makes sense to let warm up the electronic, press tuning and enjoy. Switching it on and press tuning right away makes it worse. And it takes about the same time as to let it warm up. The tuning itself takes a lot of time.
Best,
Steffan