Cooldown starts after the invulnerability period ends.
This mod works while in Archwing, provided it is equipped on the active Warframe.
This mod allows low durability frames such as Loki, Ember, or Nova to have a small window of invulnerability to cast their abilities in the open.
Rolling Guard also synergizes particularly well with Mirage, as she lacks a defense against area-of-effect attacks, and has low durability. In addition, her passive ability letting her roll much more quickly gives her more time to act while invulnerable.