It's kind of inconsistent. RMSS has Stunned Maneuvering, but the mechanic removes stun. RMFRP has Stun Removal, with the same skill description as RMSS's Stunned Maneuvering. SoHK lists both, with two different mechanics neither of which matches RMSS or RMFRP. Neither is an "Adrenal" skill. RMSS and RMFRP don't say anything about how much activity is required.
I would still make the character wait until their initiative.