Whenever publishers want!

While I personally never care about remakes or remasters, the consumers seem to say as quickly as possible. If millions of people buy the game again even if it was released a year ago, then it is not too early apparently. – Sibrenfetter

There is no “too soon” for remasters. Three years is totally fine for a remaster. So is a month because a new console came out or they figured out how to upscale it. A remake should probably skip a generation at least but, again, that really depends on when it came out. Beginning of a generation to the end of the next is a pretty big jump. – Tanzel

As an audio engineer, I think of remasters and remakes as entirely different things. Remasters are just putting more polish and shine on the entire game, bringing it up to modern levels. Some remasters are more involved— similar to how popular artists (like The Beatles) have very pronounced remasters. Remakes involve work on the individual stems and systems of the game. This can be made easier when the in-house studio is the one doing the remake.

IMO, do all the remakes and remasters you want. Even the smaller things continue to make games more accessible and enjoyable. –Gmail Dot Com