Ultimately, we can't tell you exactly how long you can leave butter out. We have no problem with leaving butter out to soften as long as it is well-covered. It usually doesn't take us more than a couple days to go through a stick anyway! We've never had rancid butter in that time.
For complete instructions, see my weekly column. Note: The vinyl melts in just a few minutes and is warm to the touch when you pull it from the 200-degree oven (don't use a hotter oven or the vinyl will start releasing toxins). You can form it by hand immediately, but use leather gloves if you're nervous. All beginners in Record Upcycling should try a bowl.
Quick Answer. Different types of plastics have drastically different melting points, which means some plastics such as polyvinyl chloride plastics can melt at as low as 165 degrees Fahrenheit, while other types such as the plastic in Teflon cookware will not melt until they reach temperatures of around 600 degrees or hotter.