When was the last time you had pain walking around? Generally I would say if its a Grade 1 and you haven't been feeling pain during daily activities you're safe to start running again (very slowly & minimal distance) after around 8 weeks.
Although obviously people heal at different rates and I'm not a medical professional, just have experience with tibial stress fractures.
Yes and no. At least in my experience.
I've had at least 3 cases of tibial stressies many years ago. Each time, I couldn't feel any pain just walking, I even walked the entire marathon in IM on the advice from my physio that "If it doesn't hurt, you're not doing any damage". So lack of pain while walking isn't necessarily in itself a guide that you're ready to run.
However, I do agree that 8 weeks sounds an adequate time to allow healing for a grade 1. It certainly was from my experiences. I was generally back in about 6 weeks, even in about 3 weeks on the last. By that time, my stressie-radar was finely tuned and I ceased running promptly incurring minimal damage.
Unfortunately, not all stress fractures are created equal. Depending on the location and the impact forces from running/walking, some fractures will compress with impact while others will cleave. The former generally heal quicker.
The good thing about stressies, if they have satisfactorily ossified, there will be no recurrent weakness.
Again, this advice is not a medical professional.