You should learn what a thermal profile is then.
If you are placing cold boards in direct contact with hot, molten solder, and you do not use a thermal lead-in profile, you can damage your boards or components.
Worse, if you do not know what temp a board is at the moment it leaves full contact with molten solder of a known temp, you need to remove yourself from that aspect of the industry entirely.
Mainly as a punishment for "jumping right in". Blind, no less. Let alone how easy it is to research and learn about.