Since the activated ability doesn’t have a tap symbol in its cost, you can tap creatures (including Gilt-Leaf Archdruid itself) that haven’t been under your control since your most recent turn began to pay the cost.
2008-04-01
The second ability’s effect has no duration. You retain control of those lands until the game ends or until some other effect causes them to change control.
Whenever you cast a Druid spell, you may draw a card.
Tap seven untapped Druids you control: Gain control of all lands target player controls.
