SOLVED. YA/MG girl finds machine that controls time [s]

[Adrian]

In the story, the girl finds this thing in a box and soon realizes it gives her the ability to slow down time.

The thing lives in her basement, or a part of the thing, and there's like this little metropolis happening where tiny workers go from Stone Age to City in a matter of days(?).

[Andy]

Possibly Markos Millions Marco's Millions (or The Boxes) by William Sleator?

[Adrian]

Apparently that's the prequel because The Boxes is what I actually read.

Thank you!

[Andy]

Glad to help.