Does anybody remember a book where a boy finds an alien watch and it allows him to time travel?

Question

When I was in 7th grade, I read a book that I absolutely loved. It was about a boy who finds an alien watch like device that allows him to travel back in time. I loved it because it showed some of the most realistic time travel after-effects I ever read. He doesn’t want to make a time jump in a certain place because it could be overgrown with trees when he arrives. That’s a very logical time travel hypothetical hazard. As he travels, time starts to unravel and become altered to the point where his siblings are put in horrible situations and/or dying. That’s also really realistic. Sundering time multiple times is likely to cause damage and things may get weird. Finally, he goes back in time to the Cretaceous Era and puts the watch back in the pocket of an alien creature visiting the primordial Earth and then returns home. I don’t remember the title or the author but I remember the cover had a picture of the boy in an abstract like depiction and the watch was a bright green. I was in the 7th grade in 2006 so it’s quite a while ago. Can anyone help me remember the title?

Edit: The boy who used the watch watched future change before his eyes. His sister ended up drowning in the tub in early childhood due to his meddling with time. The future he created had him becoming a brutal businessman who imprisoned his morbidly obese brother in outer space. At the end he goes back to the era of the dinosaurs and puts the watch in the coat pocket of an alien being and a Brachiosaurus witnesses it but it’s primite brain forgets it instantaneously.

Answer 1

You're probably looking for William Sleator's The Green Futures of Tycho (1981).

Per the Wikipedia plot summary:

The main character is Tycho Tithonus, an 11-year-old boy. Each child in his family is named after a famous artist or scientist and their parents expect them to live up to their names. Tycho himself is ... named after Tycho Brahe, the Danish astronomer. He finds a pocket sized time machine in the family's garden. He immediately uses it to change some things from the past and to visit the future. But as he travels more and more he realizes that he is turning into something horrible and it becomes a race against time to save himself and his family from his own future self.

The plot overview provided in a review by user Chris at goodreads.com contains more detail:

Tycho Tithonus, the youngest of four siblings - the other three being very talented and thoroughly unpleasant - finds a small, silver, egg-like object while digging up a new vegetable garden. As innocuous as is seems, that object is about to change everything. It is, in fact, a time machine.

It's not very difficult - it has a series of dials on one end, which you turn to set the time you want to go to. Press the other end and it's done. And Tycho does what anyone would do when presented with such an amazing device: go back and re-work an unpleasant event in his past. And if by doing so he could maybe teach his nasty siblings to appreciate him more, well, so be it. Of course, the ramifications of this act don't become clear until it's much too late.

But the past doesn't really hold that much allure for young Tycho. It's over and done with, and was never very pleasant to begin with. So he decides to go to the future, to see what has become of himself and his family. A quick twenty-year jump to April 23,2001 shows him what's in store for himself. A desperate, unhappy, bitter man, fronting for a lunar entertainment industry and reduced to begging sponsors for money.

Disappointed and upset, Tycho comes back. Later, he visits the future again - same day - only to find it has changed completely. He's no longer a sad, shapeless man but a tough, ruthless one, a man who uses his ability to travel through time to make money and ruin his family. Terrified, Tycho returns to his own time. But his curiosity can't be stopped. He needs to see a future where everything works out right. Unfortunately, every time he goes there it's worse and worse. His future self becomes a monster and a murderer, a willing agent to bring beings of higher power onto this planet.

It has previously been cited as the probable (but unaccepted) answer to two other questions: here and here.