In FarmVille, days last 23 hours. This means that any growing times listed in days must be calculated with a 23 hour day. This is in place to ensure that farmers may harvest and re-seed their crops at the same time each day—if a day was 24 hours long, crops would be ready at a slightly later time each day, due to the amount of time necessary for harvesting, plowing, and seeding. The 23 hour day has no effect on crops that take less than a day to grow, so these can be calculated normally. Note that this also applies to animals and trees.
There is a bug with puppies. A notification shows up saying for example "feed your pet in 3 hours" when in fact it's four hours - a bug almost certainly caused by the puppies using a 24 hour feeding cycle instead of 23 hours.