That makes it sound like you picked a date you can't honestly keep, in terms of releasing a working, bug-free game with achievements. So, I'd say it is more honest to move back the date, so you can release a game everyone will be happy with. A whole lot of successful games have pushed back their release dates, often at the last minute--it's totally common in the industry . People complain, but they're still happy when the game does come, and it does well.