Postcolonial criticism is literary criticism that focuses on postcolonial writers, societies or topics connected with post colonialism. Just as feministic criticism can be said to examine the position of women, so postcolonial cricism is interested in the life in a colonial or post colonial society (and individual within it). The feministic criticism questioned the dominace of man. The post colonial criticsm questions the dominace of Western nations ( so called first nations). The post colonial critics disapproves of the view that western countries are superior to others, just as feministic criticis opposes the view that man is superior to women.
As for the era of postcolonism criticism started after the WW2 and it lasts up to present time. After WW2 most of the colonized nations have regained their freedom. Many writers have written about their experience living in a colonial or post colonial society. However, the postcolonial criticism is not restricted to studying literature post WW2. On the contrary, many novels written in Victorian times, for example Heart of Darkeness, Jane Eyre etc, are today often studied and anaylized from the perspective of postcolonial criticism.
Sometimes post colonial literary works try to remake the colonial myths and even refer directly to literary works. Wide Sargasso Sea by J. Ryms is a post colonial novel that tries to re -write colonial Jane Eyre, serving as a pre equal, it tells the story from the perspective of "the other, the colonized". (It is really a wonderful novel, I'd suggest everyone to read it.)
Edward Said is considered to be a pioneer of postcolonial criticism and studies. Other notable postcolonial critics are: Kamau Braithwaite,Gayatri Spivak, Leela Gandhi, Gareth Griffiths, John McLeod, Gayari Spivak, Hamid Dabashi and Robert Young. ( the list does not end there)