According to NCAA bylaws, underclassmen must announce their intention to return to school by April 10 in order to retain their college eligibility (link). Depending on when their season ends, player may have anywhere from a month to less than a week (final four/championship game) to decide on whether to enter the draft.
One thing to keep in mind though is that the NCAA deadline is approximately three weeks before the NBA’s own early-entry deadline of 11:59 pm EST on April 29th. This creates a loophole in which a player who wants to declare for the draft can say he’s staying in school by April 10 (thus retaining his eligibility in case things don’t go well) but then submit his name to the NBA by April 29.
Also at consideration is where or not a player hires an agent. Once you hire an agent, you lose amateur status and are ineligible to play in the NCAA.
So to make a short story even shorter, we'll know whether Gorgui is staying or going on or before 11:59 pm EST on April 29th.