Fun story. I had a flip phone years ago and you could have multiple recipients to a single text. And if the text was multiple pages, it would split into several texts. And you could resend already sent texts.
So one time I put in my girlfriend’s phone number in all 20 recipient slots. I then filled the text to the max size, though I don’t remember how many it split into. I then resent it over and over. This all took like 2 or 3 minutes.
Her phone was sending notifications over and over for the entire rest of the day. I’d guess at least 8 hours, probably more.