There are some great long toss discussions on this forum. The following is what we use with our high school baseball players here in MA twice a week during the fall. It takes less than 20 minutes; our varsity players essentially take a step back every two throws once the arm is warmed up.
1. Warm up by playing light catch at 45-60 feet (3 min)
2. Throw at 60-75 feet (2 min)
3. Throw at 75-90 feet (2 min)
4. Throw at 90-120 feet (2 min)
5. Throw at 120-150 feet (2 min)
6. Throw at 150-180 feet (2 min)
7. Throw at 180+ feet (2-5 min, depending on length of distance)
8. Cool down at 60 feet (1 min) (Pitchers should spin some off-speed pitches and breaking balls)