When using an invocation, a chanter will have to stop chanting, and even restarts chanting a few seconds afterwards. It's roughly when the recovery of the invocation is about to end, but there's no clear descriptions on it. I wonder if anyone knows exactly how it works? Does action speed matter?

This means that timing an invocation has benefits or punishments. if I cast one when a phrase is about to end, I effectively lose more than 1 phrase. Casting an invocation right after a phrase ends instead costs a little more than half a phrase. It also means using 2-phrase-invocations as a skald isn't as good as 1.5x invocations.

Iirc that pause (or its length) is not influenced by anything. I'm not 100% confident though.