to convert to something you can manipulate in MySQL, use the FROM_UNIXTIME function in your query
To go the other way, there is an equivalent UNIX_TIMESTAMP function - but be aware that translation between the two values is lossy in regards to timezone mapping (unixtime should generally be in GMT).
Alternatively, look at using a library like Carbon to make time format conversions and manipulation in PHP
What I am trying to do is convert a column to unix timestamps from yyyy-mm-dd. Once I have it in the unix timestamps, I can use the xf function to read it.