First, create a folder in your Pictures folder called ‘Instaloader’.

$ mkdir ~/Pictures/Instaloader

Next create a file inside that folder.

$ nano ~/Pictures/Instaloader/instaloader.sh

Add the following to the file (replacing user’s with Instagram profile names) and save:

#!/bin/bash
cd ~/Pictures/Instaloader
~/.local/bin/instaloader --fast-update user1 user2 user3

Give the file execute permissions and run it.

$ sudo chmod a+x ~/Pictures/Instaloader/instaloader.sh

$ sudo ~/Pictures/Instaloader/instaloader.sh

If it successfully executes, then add it to cron.

$ crontab -e

# DO NOT EDIT THIS FILE - edit the master and reinstall.
# (/tmp/crontab.z5YMVK/crontab installed on Fri Mar 5 07:57:15 2021)
# (Cron version -- $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)
# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').
#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h dom mon dow command
0 0,12 * * * ~/Pictures/Instaloader/instaloader.sh