Commentary for Avodah Zarah 149:7

R. Shimon b. Gamaliel seems to state the same opinion at the previous one, the tanna kamma. Both require waiting from one season to the next, which seems to be 12 months. The Talmud explains that R. Shimon b. Gamaliel is more lenient—he does not always require waiting a full twelve months. The time could be less, for instance the time between one year’s pressing of late ripening grapes and the next year’s pressing of early ripening grapes. The time between one year’s pressing and another could also be longer than 12 months.