Context: T270032: Find a solution for cl_timestamp and T42626: Standardise type of timestamp database fields (MySQL)
This requires data migration and won't be easy, better to be done once the table is normalized (T222224: RFC: Normalize MediaWiki link tables)
It looks like we already treat this field as a standard binary(14) timestamp in the code in some places, e.g.:
That's a bit worrying. I'm not sure how that actually works. I hope it gets converted magically by MySQL when inserting and comparing, otheriwse we have a bigger problem…