Bulb Ramping is a method of using an intervalometer to make minute changes to a camera during a timelapse capture sequence–and of course this needs to be done in bulb mode. It will overall make the video that you’re trying to create have a smoother transition if you’re shooting from day to night. Alternatively, you could set the camera to an auto mode and then try to de-flickr in post, but that will overall be very taxing on your computer’s video memory. The video above shows you how to do that and tries to educate the viewer more on the method, but it also tries to pitch a new product: the PromoSystems Controller.
Make sure you have a good and fast memory card too, as they tell you to shoot RAWs.
It’s worth it to check out the entire video.