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.
Heat the lead until it melts. Turn on your heat source and adjust the heat to its highest setting, if applicable. Apply the heat as directly to the lead as possible. Lead melts at a temperature of 328 degrees Celsius (621 degrees Fahrenheit), so it will take time to melt a large amount of lead. Since most lead you use will not be pure, you will have impurities ('dross') float to the top.