I'm a long time Tamiya polyester putty user, and I read Japanese, but I've never read the instruction on it. (LOL)
Anyway, once you mix the putty and the hardener, it start hardening in 5 - 10 minutes, depending on how much you add the hardener, room temp. etc..
Working time is the time you have to mix the putty and the hardener, and apply it to wherever you want. Just use it on a scrap part, and you'll find out.