Why two different recovery elixirs can share a cooldown.
Interlude sets Mental Strength elixir reuse to five minutes. Life and Mental Strength elixirs of the same grade share that reuse: using the A-grade Life elixir also prevents use of the A-grade Mental Strength elixir during that interval.
Life and Mental Strength elixirs of the same grade share an emergency recovery window. Before using the HP elixir, consider whether you will need MP recovery during the next five minutes. Track availability with the shortcut cooldown indicator.
For a healer, check the actual recovery skills available to your profession. Invocation is stationary meditation that lowers physical defense and stops when attacked; using it safely needs a protected moment. It is not an instant replacement for an unavailable MP elixir. Prepare recovery before the party has exhausted both its consumables and support mana.