How can I encourage/incentivize students to do lab work early?
Assuming that cheating/collaboration isn't an issue, just create a sign up sheet at the beginning of the semester, breaking each assignment into two blocks. The students will most likely self-select into groups: those who want to get the work done and out of the way, and those who want to put it off as long as possible. While the relative size of the groups may be imperfect, this will just urge them to fill out the signup sheet as early as possible as well. Then you could probably handle a few case by case switches as needed and thusly manage the resources.