Eventually, they'll have a version of the file for each minute in the day. After that, the hash should ensure that no additional space is used to store the content. (I think, I don't know much about git internals.)
After that, if you assume 128 bytes per commit (timestamp, and maybe a hash or two saved?) then probably around 14 years.
Every commit will need a new tree object, containing the names, hashes, and chmod of each file/folder in the root (LICENSE, README.md, _config.yml, index.html, and bin).
I modified the script to commit as fast as possible (cycling the minutes between 1 and 60), and after 600 commits, doing "git gc --aggressive" before and after, the .git directory grows by around 460 bytes per commit.
After that, if you assume 128 bytes per commit (timestamp, and maybe a hash or two saved?) then probably around 14 years.