Your professor's wrong. Would you do that for any other cost? For the cost of labor? What happens if the project continues? Do you tell your customer, 'oh sorry, we thought the project would fail so we're going to need another $52,000 for rent'??
There is always uncertainty in estimates, more uncertainty with some things than others. For rent, especially since you seem to know the exact monthly amount, there is little uncertainty of what rent will cost for your targeted duration. There's always risk the project will cease before it finishes, but you cannot build that savings into the project's budget. Instead, because of this uncertainty, you may build in some cost contingency to cover the expense to get out of your lease early.
The only time I can think of loading something less than the $6K/month is when you think you might get a better deal at some stage in the future. You can use expected value calculations to load that possible savings in.
If you are able to put under contract the project using a progressive elaboration process, then you can firmly load the rent expense for the first portion of the project, then load the rest as you move along; however, you would still provide a target in the way of a rough order of magnitude (ROM) for the elements under future elaboration.