wordplay - Misheard and Obscured

My friend was trying to tell me an idiom he heard, but I think it got lost in translation. What he ended up telling me was this:

Bread makeup
Not harmful
Obviously
525600s

Can you guys figure out what idiom he was trying to tell me?

Note:

As it has caused some confusion, everything written is correct.
Also to be clear I simply transcribed exactly what he said to me

Hint:

s != seconds, s == s

Hint 2:

You can't apply this makeup

Answer

Here's what I got:

Wet behind the ears

Each line is

A word that has been misheard as a different word and then obscured by a synonym

Bread makeup

Some bread is made of whey, kind of sounds like wet
OP's intended word for this clue: wheat

Not harmful

Benign, sounds like behind

Obviously

Duh, sounds like the (thanks Dan Russell)

525600s

A year's worth of minutes, and year + s sounds like ears