This study examines how changes in auction timing affect bidding behavior, using data from Chinese land market transactions. In 2021, a new policy mandated that 22 cities shift from sequential to simultaneous auctions for residential land. Using an event study approach, I find simultaneous auctions lead to higher prices and a greater auction failure rate. Additionally, I examine testable implications related to the mechanism behind the policy effect: auction prices rise more for higher-quality land and in cities with higher land quality variance; moreover, the auction failure rate increases more for lower-quality land. I then developed a model of bidding that rationalizes my main findings and offers some policy suggestions.