Hi Peter, thank you for the AMA. If an H1B visa application got accepted for a start date in October 2017, how long after this start date would the person stil

Hi Peter, thank you for the AMA. If an H1B visa application got accepted for a start date in October 2017, how long after this start date would the person still be able to come to the US to work and still claim the visa? Does the visa expire if it's unused? Can they come a few months late (December 2017 - January 2018)?