The thing I hated the most in my previous internships, was to filling the timesheet, (yeah even interns needed to do that), so I’ve been pretty astonished by the beautiful and smart solution proposed by vitamins, a british design agency that I admire. It’s a physical planning, but it’s also available online, it’s easily to modify it and before everything it’s fun. Each person have is own lego character, and each color represents a project.
They’ve also done something quite interesting with the “time representation”, they simplify it to half-day. It looks like they didn’t want to complicate their wonderful project and avoid this problems, but I think it’s a way to encourage you to focus on one and only one thing during a long period. That should avoid the lack of productivity due to the change of project (it’s maybe a matter of second to open a new doc, but do you think your brain is following that fast?)