If a girl takes several hours to respond back?

So this girl I've been texting usually takes 5 hours to reply back. There was this one time where she responded right away (like in seconds) but other than that she usually takes 5 hours. Usually it is a sentence long so that's good sign. She has always texted me back too.
I've always been told that girls are literally on their phones all the time and if she likes you then she will respond quickly.
If a girl takes several hours to respond back?
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