Can either part of Sivir's Legend skill be used during the opponent's turn?

Ruling: Yes, both parts of Sivir's Legend skill can be used during the opponent's turn because they are triggers that activate whenever the appropriate event happens.

Nuances:

• You can float power by recycling runes on the opponent's turn to proc Sivir's Legend skill
• However, you cannot use the power generated during the opponent's turn, so you trade a potential energy and a power for just a one-time power