When do you pay the power cost for Bullet Time's effect, and can you exhaust/recycle runes for energy and power during its resolution?

Ruling: You pay the power cost for Bullet Time upon resolution, not when casting it. You can use reaction-speed add abilities (both exhausting runes for energy and recycling runes for power) during Bullet Time's resolution when paying the power cost.

Sequence:

• Cast Bullet Time, paying only its base energy cost and choosing a target battlefield
• Players pass priority and Bullet Time begins to resolve
• During resolution, you can exhaust runes for energy and/or recycle runes for power
• You then pay any amount of power and deal that much damage to all enemy units at the chosen battlefield

Nuances:

• If Bullet Time is countered, you do not pay any power (unlike additional costs which are paid when casting)
• Your opponent cannot see how much power you will pay before deciding whether to respond to Bullet Time
• Rule 416.3 allows using reaction-speed add abilities any time spells or abilities require resources to be paid, which applies during Bullet Time's resolution
• This works the same way as blue Teemo - the amount is not declared until resolution