In most Linux distributions using systemd, the cron.daily jobs are actually triggered by a systemd timer rather than traditional cron. The default execution time is typically set in:

/etc/systemd/timers.target.wants/timers.target

First, let's verify how your system currently schedules daily jobs:

systemctl list-timers --all
# Or for more detailed info:
systemctl cat cron-daily.timer

There are two primary methods to change the execution time:

Method 1: Editing systemd Timer

Create an override file to change the schedule:

sudo systemctl edit cron-daily.timer
# Add these lines (example for 3:30 AM):
[Timer]
OnCalendar=*-*-* 03:30:00
RandomizedDelaySec=30m

Method 2: Using Anacron (for non-systemd systems)

Edit the anacrontab file:

sudo nano /etc/anacrontab
# Modify the START_HOURS_RANGE line:
START_HOURS_RANGE=3-4

After making changes, reload systemd and check the new schedule:

sudo systemctl daemon-reload
sudo systemctl restart cron-daily.timer
systemctl list-timers | grep daily

For more precise control, consider moving the script to root's crontab:

sudo crontab -e
# Add this line for daily execution at 4:15 AM:
15 4 * * * /etc/cron.daily/your_script

Ensure your system time zone is correctly set as cron jobs use the system timezone:

timedatectl
# If needed, set timezone:
sudo timedatectl set-timezone America/New_York

If your changes don't take effect, check logs:

journalctl -u cron-daily.timer
journalctl -u cron-daily.service

In Linux systems, scheduled jobs in /etc/cron.daily/ are executed by anacron (on desktop systems) or cron (on servers) through the /etc/crontab configuration. The default execution time is typically early morning (usually around 6:25 AM on most distributions).

The execution time is controlled by one of these files depending on your system:

/etc/crontab
/etc/anacrontab
/etc/cron.d/0hourly

For cron-based systems (common on servers):

# Edit /etc/crontab
sudo nano /etc/crontab

# Find the line similar to:
25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )

# Change the time (format: minute hour)
30 4    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )

For anacron-based systems (common on desktops):

# Edit /etc/anacrontab
sudo nano /etc/anacrontab

# Look for the daily jobs section:
1       5       cron.daily      run-parts --report /etc/cron.daily

# The second field (5) represents the delay in minutes after system start

For more precise control, consider moving your script to a direct crontab entry:

# Edit root's crontab
sudo crontab -e

# Add a line like this (runs at 3:15 AM daily):
15 3 * * * /path/to/your/script.sh

After making changes, check the logs to verify execution:

# Check cron logs
grep cron /var/log/syslog

# Or for systems with journalctl:
journalctl -u cron.service --since today

Remember that cron jobs use the system timezone. To check and modify:

# View current timezone
timedatectl

# List available timezones
timedatectl list-timezones

# Change timezone
sudo timedatectl set-timezone America/New_York