Because Stefani never disclosed the song title's meaning, reviewers came up with various interpretations. In a satirical, line-by-line analysis of the song's lyrics, OC Weekly critic Greg Stacy humorously speculated that "Gwen is apparently the captain of the cheerleader squad; she is the girl who 'hollas' the chants, not one of the girls who simply 'hollas' them back".[6] The most commonly accepted meaning is that a hollaback girl responds to a confrontation with words but that Stefani would rather take initiative and "step it up". However, the term can be traced to American construction workers of the 1940s used to denigrate females that would positively respond to their "catcalls" or hollers.[7]
I don't know the song, but pass it on normally means to share something with another or others, whether keeping it for oneself also or not, especially something received from a third party. Thus, for example, if someone smiles at you or greets you, you could be said to be passing it on if you smile at or greet someone else. If someone gives you a platter of chicken, you can take one piece for your plate and pass the platter on to the next person.
"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.
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