Depends on the game. Story driven games should at least explain what the game is about, if its just a brainless fuckfest it should have a few scenes and if its a good game it should have most of the mechanics already implemented in the first release, nothing sucks more then updates without game progress.
Some sort of prologue/intro should be finished in general. Its hard to put that into a timeframe, but a 5 minute teaser is more a reason to never download the game again because it shows what to expect from updates this lazy dev will provide.
Pretty much same as above, at least an hour but should give a good sample of what to actually expect. If just story setup dev might as well wait till more content is in.
If the creator is open to feedback ... I'd take a shorter release, 30 minutes, enough to give an idea of what I like/don't like about where a game is going.
There should be enough content and story to get the played hooked.. first impressions matter the most after all, especially if you're trying to get Monetary support.
For a first release, I kind of view it as a first chapter of a book. Should be able to set the story, the premise, include a couple good sex scenes, showing off the developer's capabilities as a writer and modeler/animator, and tease a lot more going forward.
Length (time) is heavily dependent on the type of game. But one thing I really am moving away from is games that try too hard to create a lot of delicate plot intrigue or wild levels of complexity.
I know I might not be in the majority on this, but for me a simple or relatively simple story that can grow over time is better than a story that spends two hours setting the stage before anything happens. I just don't have the patience for that.
In non-adult games, the best ones always have an intro sequence that teaches you the mechanics and basics of the game while also dumping some exposition and story. So it drives me crazy when an adult game spends the first 4 hours just doing plot stuff without any scenes at all because it's a "slow burn" game.
The worst example I can think of is At Home Again. That game is on something like its 13th release and there's still barely any sex at all in it. The guy just writes wish fulfillment stuff with an endless cavalcade of hot, excellently rendered redheads. But the story is going fucking nowhere.
Agree with several others in this thread - the first release should provide enough content to set up the story and get the player interested in wanting to continue. If it does this length may not be critical, but having 1 to 2 hours of play time is nice.
It's not so much playing time as the substance... as first release I need to understand some things, like the story in broad terms, the gameplay, the possible future content. Graphics quality is not essential, unless it's downright indecent... or unfappable
I don't think there a mininum of time, but it should give you a feeling of how the game and its pacing will be. Showing a bit of the plot, characters, having nice dialogue and some good scenes.
There are games that the first update is long, and yet you don't really have an opnion after playing.
I believe it should have an hour or two worth of content at least. I dislike the games that end in like 10 minutes because you don't get to experience much