sudo crontab -e

Press i (insert text in vim)
30 19 * * 5 /sbin/shutdown -h now

Press esc (to exit editing)
Press shift+z shift+z (Writes changes and quit vim)

Time format in Crontab:
* * * * * command to execute
│ │ │ │ │
│ │ │ │ └─── day of week (0 - 6) (0 to 6 are Sunday to Saturday, or use names; 7 is Sunday, the same as 0)
│ │ │ └──────── month (1 - 12)
│ │ └───────────── day of month (1 - 31)
│ └────────────────── hour (0 - 23)
└─────────────────────── min (0 - 59)