I must be missing something, can somebody clarify or correct me?

The Thraxan guy told Mark that the journey to Earth took most of his life. Very shortly after, Mark asks how long it’ll take to get to Thraxa and the reply is 6 days. I looked up Thraxan lifespan which is apparently 9 months.

What’s the deal with this contradiction? Did the writers mess up and forget a detail established 2 minutes earlier or is there something else going on that I missed?