A federal judge reduced, by one month, the sentence of former Hono­lulu police officer Michael Steven Chu for conspiring to grow and possess marijuana to sell.

U.S. District Chief Judge Susan Oki Mollway sentenced Chu last week to eight months in jail but resentenced him to seven months Thursday because she said she erred in calculating the sentence using federal court advisory sentencing guidelines.

Judges do not have to abide by the guidelines, but must consider them when determining penalties.

Mollway also extended to April the date by which Chu needs to turn himself in to begin serving his jail term, to allow him to spend time with his terminally ill grandfather. Chu’s previous reporting deadline was Feb. 13.

Chu admitted to participating in an indoor marijuana growing operation in his girlfriend’s Kapiolani Boulevard apartment and another one in his rented Mililani Mauka home.