The postmillenial bit on the picture is not 100% accurate; there are different views among postmils about what the millennium is:
1. Some hold its a golden-age within the NT, as is represented in the graphic.
2. Some hold its the whole NT age, as with Amils.
3. Some hold its from 70 AD until a rebellion against Christendom "Satan's little season".
The main difference between amillennial and postmillennials is the latter believes that the gospel will advance much more in the NT age.
"May that happy period soon arrive when the unclouded glory of divine revelation will shine from pole to pole; when men every where will see eye to eye, in all things that are connected with divine glory, and with their own eternal felicity." William Stavely (Irish Covenanter), An appeal to light (1796), pp 143-4