It starts the remote and local checksums at the same time in parallel so if the remote checksum fails it is still committed to calculate the local checksum.
Rclone is doing a checksum check in your case because the files are the same size but the modification times are different so rclone wants to make sure they are the same or not before transmitting them.
There are lots of checksum disables rclone help flags sum to see them!
However there isn't a way of disabling this particular checksum. This was also discussed in this thread
It might be that --ignore-checksum should skip this, or there should be a new flag...