Shalom Andy, and Doves,
    Here's my simple answer....In Rev. we are told that the "Tree of Life" will bare 12 fruits, a new one every month ......this means there will be 360 days in a sequence of the trees reproduction.  And there will be 12 changes of months.  360='s 12x30.
    The reason is because in heaven...there is no need for the Sun or the Moon, because HaShem is the Light thereof.  Everything in heaven will focus on Him, and revolve around Him.  No days and nights....just a Tree of Life to measure time by!!
    Prophecy also revolves around Him, is all about His Timing...etc.  soooo...Prophetic years are also.
Shalom,
Miriam Brown