Did “300 days” mean 300 days off Purgatory?

Current norm Open question What the Church holds

No. The old figures belonged to the Church’s discipline of penance on earth, not to time in Purgatory, and Paul VI abolished them: a partial indulgence is now designated “without any determination of days or years” (Indulgentiarum Doctrina, Norm 4). Its measure is now the act itself. Whoever performs it with at least inward contrition receives, through the Church, a remission equal to the one the act already earns (N4). Neither the councils nor the Catechism give any figure for time in Purgatory.