How Long to Rest An Injury?

Not long, depending on the severity, of course. Not at all, depending on how you define "rest." For moderate-to-severe trauma, resting the affected tissue for an excess of one week is often contraindicated. Most of the initial repair is over at that point. Contraction is what stimulates growth thereafter: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3940509/?fbclid=IwAR1VK3lKLYvdGKUMStkgLB8SF8U8IgzWh78oSOEY3yKNNQMsFL_Wk9DmQIw

There was a time when broken arms and legs were cast for six to nine months. Now, seldom is anything set for more than about four to eight weeks, even on the structural damage side of the equation. Brain surgery patients are encouraged to walk the same day if tolerated. Sprains, which we once thought needed total immobilization, we now know need movement as soon as can be done without pain. In astronaut studies, we find that young people begin getting osteoporosis with just a few weeks of weightlessness. 

There's no need to push through or increase damage. But lack of movement is not the answer.