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a "steem whitepaper" have one. look at "Mitigating Timing Attacks" part
https://steem.io/SteemWhitePaper.pdf

there is citate:
"Steem levels the playing field by requiring all conversion requests to be delayed for one week. This means that neither the traders nor the blockchain has any information advantage regarding the price at the time the conversion is executed".

dont know exactly how to convert steem dollars -> steem.
I think that is done by market