Too short, they take an interesting topic, the Titanic and reduce it to looking for a dog. Juniper's role could be removed and not much would change. Atlas's story was gone and he was just there to add pages. Allie, Vic and Max have identical personalities that don't exist. All three of them are Mary Sues done worse. At least a Mary Sue actually has an obstacle. How was/were the writer/(s) unable to start the plot properly? "Stranger gives kids time machine dog swallows" is a terrible way to start a story. Would have worked better in a 20-page book. A novel this bad is horrendous, made worse by the extended page length.
It's also oddly bland, as mentioned earlier Juniper's a plot device, Atlas does nothing in the entire book and Allie, Vic and Max have no personality other than good guy. The context is extremely low to the point where there's no sense of tension. The characters themselves make it worse, only barely considering saving the 1500 lives lost on the ship.
TL;DR: It's a story lacking any focus or plot and rather starts multiple subplots to make one convoluted story clearly written as multiple separate ones stretched out far too long.