I am not very familiar with TOG, but going by the link you gave, half way through unit 3 would be the start of SCM module 5 which covers 1550 – 1850, including Jamestown 1604 and Pilgrims 1620 and early American colonists and Revolutionary War.
We have greatly enjoyed studying American history. It is ds 9 favororite subject and we read it daily. We spent a whole year on 1550-1800, & another year on 1800’s and we are currently using the Prairie Primer and Little House books. In the end we will have spent 3 years on modules 5 & 6 by adding in extras we like.