There are a couple of expressions in English that have left question marks in my brain. Just what thought are they trying to communicate? The first is, "burning the candle at both ends." Of course, that's the expression for being immensely busy. Whenever I hear it, I imagine a burning candle with flames simultaneously burning both ends of the wick. You get twice the light at twice the expense. And, you burn out twice as fast. Besides, where are you going to get a candlestick to hold such a candle? So, I suspected that it had lost its meaning as an expression.
I didn't do any special research or anything. I just turned that expression over and over in my head, trying to make it make sense. Then it came to me: So busy that they're "burning the candle at both ends of the day." Aah! Now it makes sense. That's working pre-dawn to post-dusk... pretty busy.
The other mysterious expression is, "happy as a clam." I couldn't figure out how clams were known to be happy. "Happy as a lark," maybe. Meadowlarks are birds that act joyfully and sing energetically. "Happy as a clam?" ...not so much.
This one took a little research. It turns out that the meaningful part of this expression has been lost over the years. The original expression was, "as happy as a clam at high tide," or "...at high water." (Thanks, Phrase Finder.) Having grown up on the Monterey Peninsula, I've witnessed tide mechanics. I get how high tide will bring clams their nutrients and make them happy. Now, the whole expression makes sense.
I don't think there's any need to change these expressions in your writing. I do think it's better to use them mindfully to express exactly what you want.