There is a large difference between "exactly 10 minutes from now" and "any time in the next 24 hours". This is exactly the reason that these types of spells had their duration changed to 10 minutes. Because "any time in the next 24 hours" is overpowered and breaks campaigns.
Some campaign are more fragile than others.
Given the (proposed) limits on preparing rituals, I do not see any serious issues. There's a big difference between "I can spend x thousand gold to do something", and "I can memorize invisibility five times, since I don't have any other second level spells likely to be useful".
Some people might argue the ability to cast many spells (remember, the number of rituals is only going to keep increasing) with only ten minutes prep time, anywhere, anywhen, is "campaign breaking". After all, if you didn't prepare the right spell in 3x, you have to wait 8 hours to get it, 8 hours you may not have. Ten minutes is a lot less.
Campaigns tend to adjust to what's permitted. Scry/buff/teleport is virtually useless in the campaign I'm in, for two reasons:
a)The world knows those spells exist, high level casters are common, and any enemy we face is prepared for such things and has nasty surprises waiting.
b)Villains tend to attack first. Usually when you're in a situation when combat is not expected.
I can almost guarantee you that, sometime before D&D 5.0 comes out, there will be an "official" method to cast rituals quickly.
(You can avoid many of the concerns by simply saying a ritual cannot be cast when any enemies have line of effect to you -- in short, they can only be cast "out of combat". I agree this still doesn't solve the problems with Memory Vault, which seems to be limited so as not to make it a plot-killer, and I can understan that. As written, it's more of a plot SEED. ("You wake up in an alley. You're almost dead. You have no idea what happened. Last thing you remember, you were at the Royal Ball...") NOTE: Plot seed is NOT a bad thing, and plot seed spells/rituals were one of the things I considered most greviously missing in 4e core. WOTC, IMO, released a sub-par set of core rules, but they are doing gangbusters in correcting what I perceive as their mistakes, and I am actually starting to get excited -- not just tolerant -- of 4e. Go, WOTC!)