When you go to the Coppermind for the first time, you will get a pop-up saying the wiki can contain spoilers, but it will also have a link to the Time Machine.
A link to the Time Machine is in our wiki-wide purple spoiler warning at the top of pages. (This banner won't be permanent, but it'll be up for at least a month.)
Lastly, toward the top of the left sidebar, there is a Time Machine link.
In the Time Machine, you can simply go in the dropdown menu, which has a few presets, which include: "Before Rhythm of War," "Before Rhythm of War and Dawnshard," "Before Oathbringer," "Before Shadows of Self, Bands, and Secret History," and lastly, "Before Words of Radiance." You can also select whatever date you'd prefer as well. We'll update this list with each big cosmere release.
There are a few issues with Time Machine, so it isn't flawless. If you set the Time Machine to a certain date, and you specifically go to a brand-new Rhythm of War topic, there's no "previous" version for the Time Machine to give you, so it will give you a page after 11/17. Also, when looking back on old pages, templates use their current template version. For example, the navigation box at the bottom of Stormlight pages might have additional topics. We'll try to not have glanceable spoilers there. The last issue is that the further back you go, the more sucky the wiki is. The "Before Words of Radiance" one will look really bad and have broken templates. But! For more recent things, especially OB and on, I think this will be really, really nice for most people. Do also note that for whatever you pick, there will be spoilers for other series that existed at that time.
Other things we have done beyond our usual spoiler banners at the top of pages to help with this:
1. We now have the spoiler pop-up the first time you go to the wiki, explaining that the wiki does have spoilers.
2. There were lots of reports of Google indexing some spoilers in its text previews for pages, which is not great. This should no longer be happening.