It would depend on how many minutes a day you would spend in order to read the bible. There are some who would read the bible for about an hour every day. There are also some who would read for about 45 minutes. There are also some people who are fast readers so they can finish reading the chapters in a limited amount of time.
It will always be different for all people. Just remember that if you would be following certain programs. Most of the programs would allow people to finish reading the Bible in 90 days because all of the bibles would be placed in portions.