I have nothing against part-time staff. But, if they only work until 4 PM until 5 PM, then the OOTO replies aren’t as helpful. If we had staff that only worked on certain days, then knowing that it may be more than one business day before a reply would be useful.
Like, relax. If the dates are outdated, you can probably safely assume I’ve returned already and that I’m spending my time getting back to people instead of worrying about my very clear out-of-office message. If you’re really concerned, you can contact the backup person whose information I provided IN THE MESSAGE to confirm or just, you know, text me.

Over time, I began to suspect that those who might be telling the truth (of which I suspected there were very few), would mention their relationship to the person and possibly the cause, for example “My grandmother just passed away after surgery.” The ones who left it wide open (“someone close has recently died”) led me to imagine that it could be a random person in their city that they read about in the news, their goldfish, or perhaps a distant relative who had passed away in the previous few years.
Not quite an OOO, but a former boss had an email signature that said she was doing field work so her email responses would be delayed.