I imagine your using laminated treated lumber post? Gluelam are a distinctly different product that should never be in ground contact.
Concrete cures underwater. In fact the strength will be higher. High strength precast concrete products are cured under water such as bridge beams.
If you mix it correctly (don't make it to soupy) and pour and don't stir it once poured in the hole it will be fine. Wet concrete is placed all the time underwater for bridge abutments and piers. How do you think the key west bridges were done?
However why? Most throw a precast concrete cookie in the hole and set the post on that.
The post should not have concrete place around it. It will only accelerate rot.
If you have wet ground continuously and don't plan on tiling to the base of the hole I would encourage you to use permacolumns
https://www.permacolumn.com/
Pouring concrete around a wood post will only accelerate rot and do little if anything for pullout. And if the hole is inverted cone shape (as most dug holes are) it can lead to post jacking. The hole needs to be wider at the bottom than higher up.