Labs seem incredibly important for an inquiry-based classroom.
Some teachers stop doing them because of management issues. Three days per lab is one way to plan - day one for preparation and exploration, day 2 for the actual data collection, day 3 for analysis and communication. With the class that we've been observing at Apex High School, it seems that on average the students are in the laboratory setting about two to three days a week. I think that the method of doing exploration, idea discussion, expansion, and expansion discussion in that order works wonderfully. The important part is the exploration, because it gives all of the students a common basis in the lab.