I've seen houses where the owners never dropped the price. They simply pulled it off the market.
It would depend on the motivation and ability of the sellers to lower the price. If they want to move, have to move and/or are not underwater on their mortgage, they would be more likely to lower the price.
If it's a bank owned home, then eventually the price will be lowered until the home is either sold or there is an offer. But there is no set schedule for price reductions.