When I activate the Duration Add-on, what effect does that

When I activate the Duration Add-on, what effect does that have? I was hoping that it would allow me to specify the duration's length. I want to use to the plugin to accomplish scheduling of 4 rooms. No payment option is necessary. Is there some way to have the length be unspecified? That is, a member could choose a room and then indicate how long they would like to reserve the room in blocks of the minimum, which is currently set at 30 minutes.