Strange. The Docker volume (-v) parameter creates a directory on demand and „injects“ it at given position into the containers file system.
/etc/localtime should already exist on the host and be a symlink to /usr/share/zoneinfo/Europe/Berlin (in my case). Maybe it‘s different with OpenWRT.
You could alternatively try to pass the timezone as environment variable instead. Replace the -v argument by -e TZ=Europe/Berlin (or what is appropriate at your location)
> root@NanoPi:~#docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused "exec: \"/init\": stat /init: no such file or directory": unknown.