Running 100 iterations, signing on FST-01 (Cortex-M3 @ 72MHz), it's like:

real 0m15.929s
user 0m0.973s
sys 0m0.262s

Yes, generated signature is good:
~$ gpg --verify /tmp/a1.asc /etc/motd
gpg: NOTE: THIS IS A DEVELOPMENT VERSION!
gpg: It is only intended for test purposes and should NOT be
gpg: used in a production environment or with production keys!
gpg: Signature made Thu Mar 18 08:47:45 2021 JST
gpg: using EDDSA key 91B78334699E9155A9E0651CBE352A1DCF455BFF
gpg: Good signature from "Kunisada Chu " [ultimate]