For hardcore Dragon Ball fans, the seven-volume (Great Complete Collection) encyclopedia box set published by Shueisha remains the ultimate holy text of lore. Released in 1995 shortly after Akira Toriyama wrapped up his legendary manga run, these guides institutionalized the rules, geography, and power dynamics of the Dragon World. Among these books, Daizenshuu 4: World Guide stands out as the definitive breakdown of the series' cosmology and mechanics.
The guide notes the canon timeframe for traversing the road: It took Goku roughly 6 months to cross it to reach Planet Kaio, but only a day and a half to return after his training. Significance of Serpent Road in Dragon Ball Z daizenshuu 4 page 72