A bundle is nothing but a collection of multiple movies. You can buy or rent a bundle just like you buy or rent a movie.
For a rented bundle, all movies in the bundle will be available for streaming for a specific rental duration (usually 30 days after purchase but this can vary from case to case).
Once you start the playback for a movie in the rented bundle, it will expire after a specific duration (usually 48 hrs after playback but this can vary from case to case). You can find the details about the rental duration of a movie on the respective movie and bundle details page.