I heard from my co-worker in Leiden and they were able to rent the apartment for two weeks. This is great. I really didn't want to stay two weeks in a hotel even if it did have a kitchenette.
The down-side is the apartment is in Voorschoten which is about 15 minutes by bus from Leiden. It is one train stop from Leiden to Den Haag. But what I do like it is a full apartment with fully equiped kitchen (American style refridgerator, dishwasher), laundry, etc. It will be interesting and exciting to explore a new area.
I have talked to a coworker who worked in Leiden in June. He traveled by bus or by bike. I'm not certain if I'm going to try the company bike but I might.