Dilby R. Dixon's the Time Dreamer by Tony J. Perri

The Time Dreamer isn't just full of heroism, adventure, and magical worlds, it's what Dilby was born to be. The second book in the Dilby R. Dixon's series presents Dilby with all new challenges to face. Dilby already knows he's someone special having stood up to Riley Rogers, the school bully. He has also created The Dilbonary, a secret journal of weird words, traveled to many amazing worlds bringing back souvenirs, and he's finally become a cool kid. Now Dilby will be brought to the ultimate world, to a city called Riseanfall, where all time dreamers go. In Riseanfall, Dilby will learn the truth of who he really is and what he can do with the special gifts he has been given. He will encounter a new cast of characters and a dog named Hopper who will help guide him on his journey of being a time dreamer. With new friends both at home and in Riseanfall, it's hard for Dilby to know who he can trust. But when Dilby's time at Goodwin Elementary school comes to an end at the height of his popularity, the Dilbonary gets stolen. Forced to confront another bully, Dilby enlists the help of his friends, Grace and George, as they devise a plan to do something drastic to get it back. Then, just before summer ends, Dilby's dog, Hopper, goes missing. After finding a surprising clue, Dilby sets out on a mission back to Riseanfall where he'll need more than just bravery and courage to get Hopper back and track down the person who took him.