How long is too long?
I would say 1 hour is perfectly fine.
2-3 Hours might get a few bloggers annoyed enough to blog about it.
More than a day is when you might start loosing people that are quick to jump.
If your temporary splash page predicts an accurate downtime, you should be fine.
And as you already have, noting that the downtime = new features, you might not get a single complaint!
sent by KamenLee