People need to be aware of how their time is going to be spend on something. If you tell someone something is going to take a certain amount of time to complete and it doesn't happen within that time frame, your product will suffer. People's expectations also hang on how long/short something will take. Less people will want to wait for something that takes twice as long to come out than something shorter. To give the illusion of something having shorter time to wait when it's really a bit longer, break it up into smaller increments.