There's no limit! You can make the game as long as you like~
1000 words is used as an example because I personally have done 1000 word VNs and played plenty too. I recommend checking out the VNs made for the Only One of Any Asset Jam (O2A2), because they're perfect in terms of what we think of a minimum for this jam. We'd rather have some low effort games than no effort games (as in, the dev makes the game immediately crash or unplayable), hence the minimum rule.