if they are brand new night nappies, you CAN use them after ONE pre-wash, but they won't last very long, absorbency wise.

Doing all the pre-washes (and drying inbetween) will mean that when you DO use them, they will be at FULL absorbency.

If they are 2nd hand, i would just do one wash.

If they are pocket or Ai2 night nappies, i wouldn't tumble dry the shell or pocket, but you can tumble dry the boosting/trifolds (cos there is no elastic in them).

if they are fitted night nappies, i would air dry the shell as much as possible, only tumbledrying the last bit. again, it's safe to tumble dry the fitted's boosting, cos no elastic in that bit.

i dried ours indoors, on a clothes horse, with fan blowing. When nearly dry, tumble dried for five minutes (night fitteds).

hth