How do I adjust cooking time for smaller batch of bread?
Your best bet is to use a thermometer.  Most bread is done when the internal temperature hits 190F (88c).  Some people will bake longer because they enjoy a more browned crust. If it were me, I would keep your first bake step the same.  Once you reduce the heat, the second step might not take as long.  I might check the temperature at 15 minutes to see where it is.