Just my 2cents
For hammie injuries we usually work on an intro to run week, followed by a volume week, then an intensity week followed by a full training week. This is a minimum and the time can be greater depending on the severity of the injury. Within the weeks we usually work volume and intensity days. A volume day may be 3-4 sets of 6x60m (20m build up/20m hold/20m decel). On intensity days we bring the speed up from 10m. I prefer to build the speed from the lower distances up. For example, they need to be able to sprint at 10m and hold through to 20-30m before being able to sprint 20m or 30m. The intesity of our longer change of direction work (e.g. S run) is approx 20% below straight line running i.e we reach 100% in straight line running over 40-60m before 100% in something like a 40-60m S run.