How long does it take for the spray applied cellulose to dry?

Depending on atmospheric conditions, you should wait 3-5 days after installation before hanging sheetrock. Cellulose dries from the face back towards the sheathing and loses 1/2 it's moisture in the first 24 hrs. The manufacturer, National Fiber, will stand behind 24 hour drying time. If there are significant sources of moisture in the house such as an improperly vented heating system, or a new concrete slab, the drying time may increase. If the sheathing is below freezing, or if the walls are thicker than 6" then it will take considerably longer to dry out. Cellulose can actually help wet framing to dry and it dries in a controlled manner.