Damnit, looks like I missed this one.
How likely is it that someone who invested in day 6 or 7 will see a profit? Not likely IMO. Games like this reward the early investors. If I'm not one of the people who invested in the first day or two then there's a high chance that I won't get paid. I'll just keep that in mind and wait for the next round to start.
I would have thought you'd only start to risk things by about the start of day 3?