The solar design t-square and a Method for designing reflectors for unattended solar cooking

Step 4 Concepts

The sun moves very close to 15 degrees per hour across the sky.  So if you want a 2 hour reflector, you have a 30 degree difference between the suns angle first and the suns angle at the end of its time shining on the reflector. The idea is to have the 2 lazer beams shining and meeting at a point. Your solar reflector is working if when you bring this point onto the reflector, both beams hit the target.
If only one hits the target, then you have to adjust the angle of the strip of reflector until it hits.
Preferable it should hit with just one bounce.  However it may be worthwhile to have it bouncing a few times if it increases the reflector  size sufficiently.