I am not aware of any that let you specify a threshold and analysis time with an automatic analysis mode. However, iPhone programs offer analysis modes where you can leave the engine running and just look at the evaluation to spot blunders.
Small Fish Chess is my favorite free one at the moment. It has a nice evaluation graph that will help you spot blunders.
If you want to pay for an app, check out Shredder, Chess by Christophe Theron, Chess Genius, Tom's Simple Chess Pro for some of the better apps. I think they all have limited eval versions to try before buying.
Is there a chess app for the iPhone that has the blunder check/full analysis feature like Rybka and other top engines.