yyyy-mm-dd isn't specific to MySql, yes its most frequently used there, but keep it more generic.
maybe something like 
\HylianShield\Validator\Date\ISO8601Date
\HylianShield\Validator\Date\ISO8601DateTime

Al mag iso 8601 datum officieel in de formaten YYYY-MM-DD of YYYYMMDD zijn.
http://en.wikipedia.org/wiki/ISO_8601