It's the weakest aspect of the book, but one that I let slide. I always interpreted it as Jake being slightly depressed in the present, coming off the back of his divorce. There honestly isn't anything holding him back to present day, so why not. You lose two minutes of your real life, and get to go on an adventure.
The timeline of everything in the show is a bit moved up. I think things are accelerated by about 2 years, if I'm not mistaken. Without spoiling anything big, I remember the boom having more minor experimentation with changing the future, so more back and forth between the past and present before diving into the main goal. It's not a huge loss, especially in a TV show because it probably would have bogged down the first episode. I think they traded that for a more aggressive approach to time pushing back against change.