You will always be able to stick your fingernail into cured Rod Bond. It doesn't get ceramic hard, ever. That's the beauty of it ... a truly flexible adhesive.
I mix Rod Bond in a plastic mixing cup. But the truly proper way is to mix it on a scrap piece of old wood using a folding motion. The idea is to continually fold the mixture into and onto itself a bunch of times ... kind of like kneading bread dough.
Of all the many products designed and/or adapted to rod building, Rod Bond is the most reliable and the most forgiving ... great stuff.