[twitter-dev] since - until

Hi, Is there a minimum date that can be used for since or until params in a Search API? It seems limited only to the current month? Thanks

[twitter-dev] Since, Until operator returns tweets outside the specified date range ?

http://search.twitter.com/search.atom?ands=olympics+covergirlrpp=100 contains results from the 19, and the 20th of Feb. However, http://search.twitter.com/search.atom?ands=olympics+covergirlrpp=100since=2010-02-20until=2010-02-20 still returns tweets from the 19th ? is this a timezone issue ?