Change 1000+ of WordPress Featured Images in 5 Minutes! › Forums › Questions and Answers › Need Thumbnails populated from first image in post › Reply To: Need Thumbnails populated from first image in post
You got it! Run the process again and again, e.g. month by month. The Time Filter let you define the time range to a day! So you can start with a single day and increase the period at every run as long as it works fast.
If both sites are on the same server the delay is very short and you can start with a longer time range, e.g. two weeks.
The only thing what could go wrong is insufficient disc space. The respective images will be duplicated, e.g. copied from the old place to the uploads folder of the new blog. That is necessary to be able to set an image as featured. For that it has to be uploaded into the library of the new blog. That way it has an ID and QFIP can assign the image ID with the post ID to tell WordPress that image is the featured image of that post.
Before you run the process I highly recommend you to make a backup of the current installation.