If they care, they will respond immediately (or within an hour)
I think the whole "If they cared about you, they'd take 30 seconds to reply" mindset is way too simplistic. There are a few reasons why someone may not reply in what you consider the proper time, and it doesn't mean they care about you any less.
Yes, physically typing a response might only take 30 seconds. But that's assuming the only thing involved is pressing buttons.
For a lot of people, the real time is spent thinking about what to say. Some conversations require emotional energy, careful wording, or preparing yourself mentally to engage with that specific person. There are people I genuinely care about, but I know replying to them isn't going to be a quick "Yep!" It's going to turn into a longer conversation or involve topics that I don't have the mental bandwidth for at that moment.
Life is also busy. Work, kids, school, chores, appointments, and just trying to decompress can make even opening a message feel like another task on an already full list. Waiting to reply isn't always about not caring—sometimes it's about not having the capacity to be present in the conversation yet.
And that's before you even get into ADHD, where some people open a message, compose a perfect reply in their head, get distracted, and genuinely forget they never actually sent it. But that's a separate discussion.
I'm not saying it's okay to ignore people indefinitely. If someone consistently never responds, that's different. I just don't think it's fair to measure how much someone cares by how quickly they text back. Caring and having immediate mental availability are not the same thing.
And to those who yell "they will make the time".... yes, they will.... and sometimes "making the time" is a day or so later. Because our lives aren't all the same.