Personally I think there should be rigorous UAT followed a consultation document and then a final round of regression testing .. documentation approval and then a staggered released over the next quarter - 

Seriously I would rather have something that works as it should and if that means a missed deadline then so be it ...

Surely giving something out to your users that doesn't work correctly and has more bugs in it than an Indiana Jones Movie is far worse than a missed implementation date

Paul