I just got a Fun Factory Delight a couple of days ago and have been having a similar issue. I don't want to overcharge it and ruin the battery but it's quite confusing to work out when it's done! All the information seems to be contradictory, what little of it there is. The manual didn't tell me anything so I hunted online, and I've read 12 hours to charge, or 3 hours. I've read the charger blinks, then turns solid, or that it's steady red then turns green
Maybe there's a couple of versions out there or something.
What I have personally observed, however, is that the light on the toy itself (on the control panel) blinks for a while, whilst charging, and then stops (well, it still has a very faint blink but not noticeable unless you closely peer). As this is the only change I've noticed, and the power seemed splendid when I used it, I'm assuming for now that's how it says it's done. Saying that however, the maximum time I've charged my precious for is about four hours, so maybe it would do something different after longer *shrug*
Fun Factory do make brilliant toys, I highly recommend them. Their silicone is the nicest I've experienced of quite a number of manufacturers.