Run it all week if you like, but it's not going to guarantee you are stable. IF you can't run it of course something is wrong, but there are applications out there such as Folding@home that can put more stress on your CPU than Prime95 is capable of. I have also noticed systems can be prime stable but not 3Dmark stable. Prime 95 is getting too long in the tooth to be able to judge the stability of modern CPUs with modern applications. Yes it has been updated and optimised but at heart, it's still a circa 1995 application.
regards,
Road Warrior