Learn English – Meaning of “kick out the last jam of the set”

"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.

I've looked up the entry in several slang dictionaries and there seem to be at least two meanings.

• When applied to children, that of silly and poorly educated with a whiff of mischievousness.
• When applied to adults, that of foolish and/or ridiculous.

Below are my sources, cited in extenso.

Oxford Dictionary of Slang (1998)

’erbert n British
A foolish person, a cheeky, unwashed child. For many years, in London working-class slang, Herbert or ’Erbert was used to refer to any otherwise unnamed man or boy. Gradually, probably by being used in phrases such as ‘silly ’erbert’, it came to have the more pejorative sense. There probably never was an eponymous Herbert; it was merely a common working-class name from the Edwardian era.

The Concise New Partridge Dictionary of Slang and Unconventional English (2008)

herbert noun
 1. a mischievous child or youth. Quite often heard as ‘little herbert’ UK, 1999.
 2 a harmless youth; a ridiculous man. An extension of the previous sense UK, 1960.
 3 a man in a specified field of endeavour UK, 1956

John Ayto Oxford Dictionary of Slang (1998)

Herbert (1960) British;
applied to a foolish or ridiculous man ; arbitrary use of the male forename
T. Barling: A dozen baby-brained herberts looking to face me off just to say they squared up to Kosher Kramer before the cobbles came up a bit smartish. (1986)