should i pva new boarded walls in a hot room to slow down the setting.

You shouldnt need to PVA plasterboard, it is designed to be plastered straight over. If its dragging then use a little !! water to aid the smoothing.

I SHOULD THINK IF YOU ARE ASKING THIS QUESTION IT BECAUSE YOU ARE NOT A PROFESSIONAL PLASTERER ,THIS JOB IS AN ART AQUIRED OVER MANY YEARS ,PUT THE TROWEL DOWN AND GET A PLASTERER TO FINISH IT PROPERLY, BEST ADVICE GIVEN ALWAYS

Plasterboard is designed only to take plaster, water based p.v.a will compromise the integrity of the outer layer of the board!!!!!!!