1. how often and how long a model streams live each day - the more frequent a model streams live, the more her earnings will rise since she is treating this as a 'job' which is what it is
2. quality of her video stream - a model with a crystal clear video stream will see more paid sessions; poor quality stream will have less paid sessions
3. quality of show provided to clients - this will determine repeat clients... or not
A model working a few minutes here or there will average little to zero. This is not a get rich quick scheme, it is a serious job and those that work it, reap the financial benefits.
Models get out of webcam modeling, what they put into it.