Fine with me. Is this an age thing (I'm 39)? Most of my friend always have their phones on DND, answering usually in a couple of seconds to minutes but sometimes hours, sometimes days... There is not real expectation to answer fast. If you call they do call back soon, usually, or they pick up. Somehow I also find chat apps to have low priority compared to a call. Still I can't imaging a call being high priority, never really been in that situation... At least, unless we are about to meet and didn't pick a date or exact time yet.

Anyway, if any of my friends would be offended by being ignored for some hours, they're going to have bad time in our group.