While we don't know the exact date that Geordi got the implants, we do know that in Star Trek Generations he had the VISOR, and then in Star Trek First Contact he had the implants. One could assume that given the events of Generations, where he was captured and his VISOR was turned into a spy camera, that he got tired of this happening (it wasn't the first time his VISOR was used against him) and opted to upgrade to the implants.