Well, if you are looking for an effect on the map, then all you need to do is use an event like this:
Set Move Route: Player
Increase speed
Wait: 7200 Frames
Set Move Route: Player
Decrease Speed
THere are 60 Frames per second, so 7200 frames = 2 minutes.
Anyway, that would work. If you wanted an item to have that effect then all you'd need to do is put it in a common event and have the item call the common event.
If you are looking for effects in battle, then making them have real-time limits doesn't really make sense, unless you are using a different battle script, in which case: link?