When loading the source-tree view of a repository, all of the last-modified dates are displaying "Just now", and as time ticks on they tick with it - to "... seconds ago", "... minutes ago", and then a refresh goes straight back to "Just now".
I took a quick look at the page, and I'm guessing this is the endpoint that loads in the relevant data: https://bitbucket.org/xhr/source-lastmod/USER/REPOSITORY/LAST_COMMIT however this just returns divs without any data, e.g.
<div data-for="#sourcelist-date-ac52dab53b4fa277ecf60644f5667270cd40ad40"><time datetime="" data-title="true">unknown</time></div> <div data-for="#sourcelist-text-ac52dab53b4fa277ecf60644f5667270cd40ad40"> </div>
Go to the source-tree view of a repository (easy :D)
The last-modified date shows when the files were indeed last-modified.
The last-modified date simply states "Just now".