1) Prime solar cooking time is between 10:00 a.m. and 2:00 p.m. (It's not likely going to work so well if you start cooking after 3:30 p.m.).
2) You need a clear day to be successful at solar cooking. (In my defense, there were hardly any clouds in the sky when I started).
3) If you are going to attempt solar cooking, start with a simple, non-temperature dependent food like rice, water, or cinnamon apples. (Rolls aren't such a good choice for the first time because they might rise and then fall when temperatures drop because of incoming clouds. In fact, I'd recommend waiting to try baking until you've master basic solar-cooking skills).
4) Solar cooking is like crock-pot cooking. You should choose foods that cook well at low and slow temperatures.
5) Small food pieces cook more quickly than large ones.
My first attempt, as you might have reconstructed from my comments above, was rolls. This was a huge mistake because I didn't know anything about solar cooking. Yet. I tried starting them at 3:30 p.m. with rolling clouds in the sky. The attempt was aborted around 4:30 when those clouds blocked the sun and the internal temps starting decreasing instead of increasing and the perfectly risen rolls fell.
The next day I attempted brownies (with powdered eggs to ensure safety). I also modified my solar cooker design (watch for more information about this modified design), started earlier in the day and made sure the sky was completely clear of clouds. After two hours, we had yummy brownies that were almost done. My third attempt was baked apples started right after the brownies. At this point, I abandoned the internal temperature probe and just let them cook. They were tender and delicious after three hours or so. The sugar had not caramelized though - just dissolved.
My most recent attempt was potatoes. I put them into the solar cooker around 10:30 a.m. and let them cook all day. I pulled them out just before dinner and was rewarded with billows of steam and a wonderful rich smell of rosemary and dill. The potatoes were definitely done. My only complaint is that the top layer of potatoes darkened and didn't look very appetizing. A little research reassured me that this was normal and they were completely safe to eat.