If I start now, I'll be about 75 years old by the time I build a portfolio of 6-month exposures. Of course, that's without considering the stuff that goes onto the reject pile. Guess I'd better start working on reducing my failure rate if I want to attempt a project like this one
Here is where it pays to be a computer nerd; you then instantly think of multi-processing.
Take several -- e.g. 10 -- 6-month exposures in parallel, then pipeline new exposures every week for 26 weeks.
With merely 260 cameras, you can then have a 260 picture set to select your portfolio from, and all in just a year!