I've encountered the phrase I can feel your heart beat in and out of time in the song Call To Arms, Angels And Airwaves and can't figure out what it means.
Does it mean that the heart beat is timeless? Or that it is constant (throughout eternity)?
"In time" and "out of time" can be a musical reference, referring to a time signature. Especially in pop music, "time" refers to the beat of the song.
For example if a musician says,
You are playing that rhythm out of time.
It means you are not playing the correct rhythms, maybe playing in the wrong time signature or adding / dropping a beat, or playing too fast or too slow.
When you are surprised, startled or scared by something, we say your heart "skips a beat".
When a heart beats in time, it is beating with an even rhythm.
So to answer your question, my interpretation is that he's making a poetic phrase which includes sentiments of being startled, but safe with the support of a loved one.
