As I've generally understood it, Kith blessings, unless otherwise stated, are used as reflexive actions or are just automatic bonuses. Overall, it largely depends on the individual kith.
Steepscramblers don't need to activate anything, just just get a +3 bonus to climbing rolls automatically.
Broadbacks can spend Glamour to add +2 to Stamina pools for a scene. Spending Glamour is reflexive.
Skitterskulks can triple their Defense when they Dodge, but Dodging is an instant action.
Venombites can spend a Glamour to make a poisonous touch attack. The Glamour is reflexive, but the required Brawl attack to touch the target would be an instant action.