Would that be 1cm thickness or square cm?
Umm, neither? 
It’s actually 1hr per mm of thickness. I’ll fix the original post. Glad you asked so I could catch the error.
S0 3mm would take 3 hrs,right?
Correct. You can push it. Folks will often go for an hour and call it good. It’s not truly annealed but it’s often enough to keep small holes from cracking.
Thanks