Rosh Hashanah 10: Six Hundred Years and One Day

If one plants or grafts in the time right before a shmitah year can affect the timing of orlah. 30 days before Rosh Hashanah may count as a year, but what if the coming year is a shemitah year? And what if it's less than 30 days before Rosh Hashanah? Also, how far can one day be extended? Does it count for a year or only for a month? Plus, the position that the world was created in Nisan, not Tishrei.