It takes me a very long time to complete one block (about an hour). It seems it's not the sewing that is the slow part, it is the pressing. It takes a while for this:
Horizontal seams straight after stitching
to turn into this:
Horizontal seams pressed with seams rotated to sit flat
Although those two photos were taken only 10 minutes apart, so perhaps it doesn't take me as long as it feels.
It took me another 12 minutes to get to this point:
Next step: assembling border sections.