Deleting all but last 5 min of data

I am trying to delete entries over 5 min old. Looking at SQLite's datetime function I attempted :

DELETE FROM MyTable WHERE TimeStamp < datetime('now', '-5 minutes')

This erases all data however, not just last 5 mins. When using a datetime object (toString()) it does nothing. Does anyone hav开发者_开发问答e a solution?