Noir: Abilities which last three turns can stack with abilities which last one (Byregot's Blessing is 3 turns of +100% Q and Magnum Opus is 1 turn of +150% Q). However, a 3-turn will overwrite a 3-turn and a 1-turn will overwrite a 1-turn.

Also it is most likely Careful they use because of the base Q gain but I cannot say it for sure