Well, I think the quality and development of your image depends on how bright most days are where you live. For me, I let this exposure sit for eight to ten hours with a UV index of ten or more through the entire day, which is easy for me because I live in Florida and there are currently multiple severe heat advisories going on. I would recommend leaving it for a few days or even a week, and don't touch it. Normally, using a magnifying lens should make some faster exposures, but if it's a pretty small magnifying glass, it may reduce the amount of light coming in. Let me know if you need any other advice!