Girl time travelled using a clock. Read in the early 90s

I seem to be the only one who remembers this but I'm sure the story was set in England (possibly wrong about that though) and main girl was slightly spoiled and a bit of a brat.

She accidentally travelled into her own future and saw that it was quite bleak due to her being a bit nasty in her present time. The time travel was all down to a clock she had.

She obviously came good, saw the error of her ways and changed her life around.

I've been trying to find this for years!!

Help please! :)

Was it new in the early 1990s?
What sort of clock?

WorldCat.org search
Search results for 'su:time travel kw:clock' > '1950..1995' > 'Book' > 'Fiction' > 'English' > 'Juvenile'

Mr. Z and the time clock
Author: Bonnie Pryor
Publisher: Minneapolis, Minn. : Dillon Press, ©1986.
When twelve-year-old twins become owners of a time clock, they begin traveling back and forth through time, trying to solve the mystery of the strange Mr. Z who is a sinister presence in their lives.

Changing times
Author: Tim Kennemore
Publisher: London ; Boston : Faber and Faber, 1984.
The strange alarm clock Victoria chooses as her fifteenth birthday present rearranges time and gives her the power to discover the cause of her parents' neglect and her mother's desperate unhappiness.

You can also try Google Books advanced search.

Changing Times!!!! That's the very one! I honestly can't believe how quickly you found that, thank you so much.

I'm going to order a copy of it now.

I honestly can't thank you enough!

Hah! Wow, I'm glad that was the one!

Well done!

Touchstone add: Changing times.

It definitely is and I've already ordered my copy!

Honestly, it's been annoying me for years and I only found this site this morning. If only I'd found it years ago!

You've no idea how ridiculously happy it's made me. A good start to my working week!!

That is entirely the response I like to see, you've made my day. :)
There's nothing like being reunited with a childhood book! Honestly I had no idea that was the one, only did a lazy quick search... though I did recall the author was probably British (and the publishing details obviously helped).

Cover image here. I like that one. It would be interesting to see what the Magnet edition looks like; they tend to have good covers.

PS. I added it to this time travel list: Time travel -- children's/young adult fiction

The book arrived and I'm loving it all over again!! It'll be getting passed on after I've finished it too :D