You use the app as you normally would. Set up your phone in the location you want, start the time lapse with the desired snapshot interval period and leave it. TimeLapse will now create a sequence of photos that will give you a record of everything that happens in view of the camera. For example, you could use it to monitor the office fridge to see who's eating your lunch.
Keep in mind this is "ad-hoc" as in improvised. It's not the designated purpose of TimeLapse but it can be useful when nothing else is available.