It is all in organizing a process. That and sewing for about 8 hours a day. I did 6-8 stars at a time on the Buggy Barn one. Sewing it all together was a snap.
The other was chain pieced and kept in order. I worked on about 5 blocks at a time and did things like sewing the same seam 5 times, trimming and ironing all five, and then sewing on another piece to each. Mindless work.
Hardest part was keeping all the on point filler triangles in the right place. I had to rip out several times. I might just have been too tired.