The ability to express preferences for specific tasks in multi-agent auctions is an important element for potential users who are considering to use such auctioning systems. This paper presents an approach to make such preferences explicit and to use these preferences in bids for reverse combinatorial auctions. Three different types of preference are considered: (1) preferences for particular durations of tasks, (2) preferences for certain time points, and (3) preferences for specific types of tasks. We study empirically the tradeoffs between the quality of the solutions obtained and the use of preferences in the bidding process, focusing on effects such as increased execution time. We use both synthetic data as well as real data from a logistics company.