If you time travel your turnips rot. Prices change at 6am and midday, but sometimes (rarely) prices change several times in a day. I've been playing while I search for a real world job, so lots of time on my hands.
Somebody I met on the island visited and kept asking questions when I tried to follow them around. While I was giving a reply they moved away. Spotted that they were picking up hybrids when I wasn't about so I flipped the wifi switch to throw them out.