When rendering an animation in the render window on the top right you can see the render time of the last frame. But where can I see the sum of the render times of all frames?
There's an add-on called Render Time Estimation that will do that for you.
Full disclosure, I wrote that add-on.
1 - Move cursor over a progress bar, it displays Estimated and Elapsed time. But it disappears after rendering.
2 - or you can check file info and calculate total (elapsed) time from "created" to " modified" time for you, if minutes are enough for you. Like here rendering took 4 min.