There's no set timeframe. Development times of years are quite normal for games of this type as I'm just one person working on it part time. There's usually an update every few months.
The engine needs the config and global files too, if you're not saving those, that's why your save files aren't working. Fortunately. there's a workaround, you can start a new game, save it as soon as you're able, then copy your old saves across, overwriting the save you just made. They need to be in the same save slots, as this will create new config and global files that will be looking for saves in those slots. So if your current save is 0001, create a new one in slot 1.