Mishra's Groundbreaker

The ability’s effect has no duration. The affected land will remain an artifact, creature, and land until the game ends, it leaves the battlefield, or some other effect changes its types.

Wotc — October 01, 2008

A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.

Wotc — August 01, 2008