Django model for datetime availability
On the item's model, add two datetime fields, for example "bookedStart" and "bookedEnd". And have a function isBooked() that checks if a given datetime or the current datetime is in that time frame, and return True if it is, or False otherwise.
If the users should be able to add multiple time frames (at once) when an item is available or not, you can make a separate model for it, for example BookedItem, and add in it start and end datetime fields, and foreign fields to the user and item. And again, a isAvailable() or isBooked() function.
I'm developing a sample application to book items from other users. I have hit a road block as I can't seem to figure out how to model when item is available to be rented. 
Requirements:

Users can rent item per day or per hour. 
Owner is able to select dates, hour an item is available.

Any ideas?