When does God punish a servant for a sin: is it from the first time, or later?

In summary, the one who repents from sins will not be punished in this world or in the hereafter. As for the one who persists in their sin, they are subject to Allah's will; He may punish them in this world or in the hereafter, or He may forgive them, except for polytheism (shirk), which Allah does not forgive for its perpetrator.