I installed & activated Sandbox on my localhost WAMP (WAMPServer) server. I have a test-site with 430 posts and 260 categories.

But, Sandbox was not too happy. It issued 2 errors, in the early steps described above by Sarah. They were:
Warning: array_slice() expects parameter 1 to be array, null given in C:\wamp\www\wp3\wp-content\plugins\sandbox\admin-table.php on line 122
This message appeared at the top of the opening screen, after "Sandbox" was initially select in the Admin menu bar.
Fatal error: Call to undefined function sandbox_edit() in C:\wamp\www\wp3\wp-content\plugins\sandbox\admin-menu.php on line 29
This message was appended to the "Of course I've backed up my site!" reminder, in the second screen, which is produced after pressing the Add New [Sandboxes] button, in the first screen.

These issues could very well be simply minor matters associated with the localhost environment. I have not looked at the scripts, but may be able to this evening.

Interesting tool. In a localhost [I am hopeful that], time-out & loading issues may be either absent, or 'freely' resolvable.