Zero delay as it just means CLN writes to two database directories at once.

Could only see it causing any delay if you had horrendously slow disks, but other than that it's not a bottleneck in any way!

Here are the docs, works well as a systemd service or in Docker:

https://lightning.readthedocs.io/BACKUP.html#sqlite3-wallet-main-backup-and-remote-nfs-mount