If you're making a wood deck using pressure treated wood then you need to wait until the pressure treated wood is dry.
So for example if you just completed your wood deck with pressure treated wood and need to seal the pressure treated wood deck then you can usually seal the pressure treated wood deck within 60 to 90 days unless the pressure treated wood is dry enough before them.
It depends on your climate as the hotter it is out the sooner the pressure treated would should dry enough to seal it.
That goes for any other pressure treated wood project.
You can seal the pressure treated wood as soon as it gets dry which is usually 60 to 90 days but can sometimes be as soon as 30 days depending on the outside temperature and humidity.