User blog comment:BannedLagiacrus/Monster Hunter Ecological and Lore Info Blog/@comment-2123858-20160512042625/@comment-25119729-20160513195941

The existence of the dunes in 4U is already prove that atleast inbetween FU and 4U time must have passed, since the dunes are supposed to be an older version of the old desert. So yeah, games taking place in different times is atleast for two confirmed.