It's based on how many rings the system perceives, even if your phone doesn't ring for you that many times. If you need or want it adjusted, that can sometimes be done by contacting the voicemail provider (usually your cell carrier). You may find some codes to try doing this if you use Google and search for "carrier name change rings for voicemail" where 'carrier name' is replaced with your carrier's name.
If you need additional help or have more questions or details to share, please join the site so you can reply in this thread. See
this link for instructions on how to join Android Central.