This little python script reads an image sequence, extracts the date and time and from exif, and prints in on the frames. This way you can see how the time passed by during your timelapse, even if you slow down - speed up parts.
Example work: https://www.youtube.com/watch?v=6V-ufYTUays
Credits
I started of from this code: https://www.amphioxus.org/content/timelapse-time-stamp-overlay Which used the filename to get the date.