Ah, so it's only when we're using the reversed order (года три) that the preposition goes in the middle? In other words, the preposition will usually be just before the number?
e.g.
Передача закончится через
двадцать минут.
The program will end in twenty minutes.
Передача закончится минут через
двадцать.
The program will end in
about 20 minutes.
For some reason I find this fascinating.
