Like so many startups in the 2014 wave, Dailymile closed some time in 2018 after failing to receive a buyout offer.  The website still loads, but users can no longer log in & there's no way to retrieve your data.

Some experiments revealed a way to get a JSON of a certain number of workouts for a user.

http://www.dailymile.com/people/heroineworshipe.js?max_id=99999999&page=0

Merely incrementing page gives another certain number of unique workouts.  The JSON is a single block of HTML.  Searching for all the entry_workout_ tags gives each workout.  For each workout, there are a number of links to the same URL which gives the complete commenting & details:  /people/heroineworshipe/entries/29741160

While the details page doesn't give an exact date, the HTML does in the abbr class="published" block

A simple C program should be able to recover all the data by flogging the server.  The trick is what format to store the data in.  Most likely, it'll go into a comma delimited text file which can easily be imported into a spreadsheet, but the comments have many linefeeds.

Then of course, there's more data on mapmyrun.  Lions ran truly epic distances in those days, but more slowly.  The theory in those days was to run long & slowly.