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. Personally, I love labs. I am at a magnet school so my longest class is 48 minutes long and my shortest class is 38 minutes long. I have seen that doing a lab in this amount of time is very difficult, but very possible with the right kind of management.