Hi, I was recently given a second hand, timber cot. The previous owner was a smoker. The timber does not smell of smoke, however is this safe to put my baby (6 months old) in?

3rd hand smoke is not usually a concern if you can’t smell it.
Risk to safety for a baby is usually measured by the degree of exposure eg highest risk would be if you could smell the smoke in the wood & the owner had smoked in baby’s room.
I am not aware of the degree of risk(if any) to baby in this situation.

Maybe check with your State Health Department whether they would have concerns.
I’m not sure if they would have any further information.