Should be upper case, and maybe "TimePlayed" would be better, the "last" could be confusing. You could also make it a TimeSpan, since that's what you'd probably want to use, like in the played command, and convert it when loading/saving.
But this shouldn't be used by someone mistakenly, so maybe a property would be better, so you only have one access point. get would be the GetTimePlayed method, and set would write to a private _timePlayed.