Does Teemo Strategist trigger when revealed after an opponent moves a unit to his battlefield, or has the window for defend triggered abilities already passed?

Ruling: Teemo Strategist will still trigger when revealed after an opponent moves a unit to his battlefield.

Sequence:

• Opponent moves a unit to Teemo's battlefield
• Teemo is revealed from hidden
• Teemo gets defender designation during the first cleanup (which happens essentially right away)
• Teemo's defend trigger activates