this was just a suggestion as feel this is an often needed thing, if you notice that all images in a shooting lost their capture time, Then it is a pretty good approximation to set them 1 min. or 10 sec. or whatever apart. Exifer is still in use - even though not maintained for years - because of this feature.
For you it is easy to implement, you just need another mask for the incremental time with ..days, hours, minutes an seconds in the same dialog. That's it (well, you need to add that time-shift for each image...)
I am sure exiftool can do it, it can do most everything. However the ease with which you can sort according file names (or whatever) in ExifToolGUI and the visual feedback for the sequence would be just great.
Again, this was just a suggestion.