Snapshot.schedule not available in 3.8

The snapshots.schedule parameter is not available in my environment
Is there something missing?

$ lxc version
Client version: 3.8
Server version: 3.8

$ lxc config set vB01-xxxxx 
boot.autostart                           limits.memory.enforce                    nvidia.require.driver                    security.nesting                         user.vendor-data
boot.autostart.delay                     limits.memory.swap                       nvidia.runtime                           security.privileged                      volatile.apply_quota
boot.autostart.priority                  limits.memory.swap.priority              raw.apparmor                                  volatile.apply_template
boot.host_shutdown_timeout                       raw.idmap                                      volatile.base_image
boot.stop.priority                       limits.processes                         raw.lxc                                  security.syscalls.blacklist              volatile.idmap.base
environment.                             linux.kernel_modules                     raw.seccomp                              security.syscalls.blacklist_compat
limits.cpu                               migration.incremental.memory             security.devlxd                          security.syscalls.blacklist_default      volatile.last_state.idmap
limits.cpu.allowance                     migration.incremental.memory.goal        security.devlxd.images                   user.meta-data                           volatile.last_state.power
limits.cpu.priority                      migration.incremental.memory.iterations  security.idmap.base                                  
limits.disk.priority                     nvidia.driver.capabilities               security.idmap.isolated                  user.network_mode                        
limits.memory                            nvidia.require.cuda                      security.idmap.size                      user.user-data 

$ lxc config set vB01-xxxxx snapshots.schedule 18 0 * * *
  Set container or server configuration keys

  lxc config set [<remote>:][<container>] <key> <value> [flags]

  lxc config set [<remote>:]<container> limits.cpu 2
      Will set a CPU limit of "2" for the container.

  lxc config set core.https_address [::]:8443
      Will have LXD listen on IPv4 and IPv6 port 8443.

  lxc config set core.trust_password blah
      Will set the server's trust password to blah.

Global Flags:
      --debug            Show all debug messages
      --force-local      Force using the local unix socket
  -h, --help             Print help
      --project string   Override the source project
  -q, --quiet            Don't show progress information
  -v, --verbose          Show all information messages
      --version          Print version number
Error: Invalid number of arguments

It is available, though looks like the new keys didn’t make it in bash completion.

The error you’re getting is because of missing quoting, you should use:

lxc config set NAME snapshots.schedule "18 0 * * *"