“How long does a muscle strain take to heal?”

The healing time for a muscle strain depends on its severity. Mild strains (Grade 1) typically heal within 1-2 weeks, while moderate strains (Grade 2) can take 3-6 weeks. Severe strains (Grade 3), involving a complete tear, may require several months and sometimes surgery. Since your son feels pain when running, it’s likely a mild to moderate strain, but a doctor or physical therapist can confirm the severity.
To promote healing, ensure he rests, applies ice, and avoids activities that cause pain. Gentle stretching and strengthening exercises may help once the pain subsides, under guidance from a healthcare professional. Proper care can prevent re-injury and get him back on the court safely!

Typically 6-8 weeks with a proper stretching and strength program.

It depends. How bad is the injury? He should see a physical therapist for an evaluation

Although a simple question, the answer is usually complex and relies on a number of factors. As a general rule, I would expect a grade 1 muscle strain to heal (without a subsequent re-injury) within 8-14 days. A grade 2 muscle strain I would expect to heal within 4 weeks and if there is a grade 3 or higher, it could be a couple of months.

Calf sprain takes anywhere from 2-6 weeks to heal depending on the level of injury without any therapy taken.