In a visual novel, for example, each update could be a chapter of your story. Each chapter could be something like 8k-10k words long (about 1h of content, so it's less likely that someone will complain about it being too short) and contain some h-scenes.
In other types of games, the number of h-scenes (interactive or not) might be the main aspect of each update and the number of them will depend on how long it takes you to build each one.
Ultimately, this will be a completely arbitrary decision on your part. Depending on the tools used during development, you can easily keep track of the amount of dialogues, scenes, etc.