When I plant wheat seeds, they have a chance to grow instantly. It sounds cool, but it gets really annoying when you have a large enough farm and you just want to plant and be on with your business. 
How to replicate: start planting seeds and it will randomly grow instantly. 
From my experience, you can increase the chances if your world  is lagging due to higher numbers of entities in the area. I had a cow farm with at least 50 cows crammed in a 1x1 area causing some lag and when I farmed, the instant growth rates increased to almost every 3-7 seeds planted.