My original idea was to release a mini-version whenever I added enough material. But the situation became more complicated after I switched from pure Ren'py code to adding Python. Now, virtually every change requires a complete restart of the game, and doing that is a pain in the neck enough for me, let alone a player.
So before releasing a new version, I decided to wait until I get to a point where a player can play a relatively large portion of the game. That way I can make changes and additions to the game while they have something to do in the meantime.