The link I provided quotes the data sheet for that product.
“Stable data should be got at least 30 seconds after the sensor wakeup from the sleep mode because of the fan’s performance.”
I have also personally measured and observed the measurements change rapidly during the warm up period for that particular device, which you can see in this post.
Again, not claiming it applies to this device, but it’s a thing for similar devices (edit: and I see in the chat it appears to now be confirmed for this device).