Meaning – What Does ‘I Can’t Agree with You More’ Mean?

'Wherein' is generally only used in formal writing. The Oxford English Dictionary gives the following senses and quotes. I have given the most recent quote, from which you can tell that the word is no longer generally used.

1. In what (thing, matter, respect, etc.)?

   1891 - Oh, Britannicus! wherein have we offended?

2. In which (place, material thing, writing, etc.)?

   1888 - Peering keenly into the shadow wherein she stood

3. In, at, during, or in the course of which (time).

   1819 - Length of days Wherein to act the deeds which are the stewards Of their revenue.

4. In which (matter, fact, action, condition, etc.); in respect of which.

   1889 - There began a round of pleasure for Julia wherein she was the central figure.

5. Into which.

   1585 - We came to an anker very nigh the castle, wherin when our patrone would followe vs [etc.].

"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.