I do the same. It's fine. :)
Each snapshot is accompanied by a note of what you're working on as well (if you make one). If you're dealing with a client who'd question that, AND not accept/understand explanations, then you'd be dealing with many more problems from them as well, particularly without a work diary.
It's been years since I've been an employee on any sites like that, but I still think the system is pretty bad. Just start with small projects and then scale up for high performing freelancers and don't offer repeat work to low performers.