I just want to be sure that leaving it de-strung for a while (I'm talking 24 hours at most) before putting the new strings on won't have any harmful effects.
Will it?

Thanks in advance.
It should be fine for such a short period of time. But why will it take you 24 hours to re-string?
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It will be perfectly fine. No worries
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Actually you should detune your acoustic after playing it every time to release tension from the bridge. If you keep an acoustic in tune all the time you can warp the guitar. Electrics on the other hand are made to stay strung and tuned. if you don't then the neck can warp.
That's what my uncle told me. And he is a Luither so I trust his advice. Apparently the reason is the top of acoustics is made of a thin layer of wood that can warp under stress from the strings over time. Solid body electrics don't have this problem, he told me that they actually have the opposite problem. The necks can warp if not under tension.