The Cam goes to sleep after each shot, when the interval is longer as 5 minutes. This is necessery for example if you shoot all 15 oder 60 minutes 1 PIcture the whole day or night. Otherwise it would be finish after 4 hours (Battery empty).

YOu have to import it to a Video-Software like Premiere Pro to create a Movie. But it should be easy.

I think most reliable way of capturing 24 hours or more is to use an external battery pack or mains power and let the camera stay on for the whole time without sleeping.

I've used GH2 with 12v car battery, 12v to 9v transformer, a DC coupler and a JJC intervalometer. Depending on car battery AH capacity, it can stay on for up to a week. Even more is possible with very large 12v batteries.

When using lead acid batteries, one thing to remember is to use a drain protector between camera transformer and battery, or else the battery might get completely drained and can't be recharged anymore. Cheap drain protectors are often available at stores that sell 12v car refrigerators and other car accessories.

Of course other kinds of high-capacity external batteries will also work well, car batteries are just one of the most affordable options.