They especially don't show long travel times, but in the books travel is usually counted in weeks or months. Also, in the books they usually travel at ~0.3g for the sake of Martians and the Belters, who are mostly not comfortable with Earth's 1G.

(This is not merely a detail, it's one of the core plot points of The Expanse, as tolerance to gravity is what makes Martians and Belters almost a different species from Earthers; the former can not live on Earth, and so they don't care much about it.)