A kids / teen book about time travel, based on a massive clock (or clock tower)

I probably read this book about 20 years ago, and I haven't been able to find it no matter how much I Googled! I think the protagonist was a boy and his sister, but my memory is horrid. There is some sort of mission to beat the clock in an angsty game of time travel manipulation, I think it ended off with the clock tower being destroyed.

I read a lot of Nancy Drew back then, but I couldn't find a link there either. TIA!

EDIT: It had a creepy element. I also read a lot of RL Stine at the time, I was never able to link it to Goosebumps, but still possible!