Not the scroll bar in the browser, the very light blue bar on the right side of the page.
You can also click the time notation there.
For the Signal Strength Heatmap it says “Jul 31” and “18h ago”.
Signal Strength Heatmap - #194 by caius
Oh you can also modify the last number in the address bar, it’s the index of the post you are viewing in the current thread.
The thread linked above has 194 posts, you can modify that number to get to the corresponding post.