Jim wrote:
I'm just redecorating a room in my flat and have had to unscrew a
window from its frame to do some external repairs and replace a broken
pane since the window is not very accessible from outside.

I used putty, didn't realise how long it takes to set.

I obviously want to paint the putty to waterproof it when it has set.
However, I can't do that with the window in place (hence why I took it
out in the first place).

Is there any way I can speed the putty drying process - (say with a
hairdrier perhaps) - so I can get the window back in place sooner?

Or alternatively, is it ok to paint the putty before it has completely
set.
with oil based paint, it should be OK.
With water based paint, it doesn't really work.

A hairdryer won't really do anything positive.
If you could lie it down flat, and heat to 40C for a week, it may work
better, but it won't really set easily.