If you want something done at a specific time (down to a minute’s resolution) with a repetition, then cron is the best.

# Run as root
sudo crontab -e
# Can also run as any other user
sudo crontab -u emaus -e

This will then open up the crontab in an editor. Add the following to run a script called /home/emaus/service_pi_led_function.sh every minute of the day.

# crontab
# m h  dom mon dow   command

* * * * * /home/emaus/service_pi_led_function.sh

N.B. 1: Make sure the script to be run is executable 🤓 (chmod +x <script>). Debugged by using text logging.
N.B. 2: The cronjob is not updated until you exit the crontab editor. Debugged by using crontab service logger.
N.B. 3: Make sure that the crontab has the correct PATH set up (see this SO answer, or my final crontab)

>>Sunrise/sunset

If you want something done relative to sunrise/sunset, then sunwait by risacher on Github is perfect.

git clone git@github.com:risacher/sunwait.git
cd sunwait
make
sudo install sunwait /usr/local/bin/

Testing the program at night with the coordinates for Stockholm yields:

$ sunwait poll 59.3260668N 17.8419725E
NIGHT

This could be combined with getting approximate location of your own IP address and then inputting that. E.g. ipfy.org has an API for getting your public IP address, e.g.:

$ echo $(curl 'https://api.ipify.org?format=text' -s)
80.216.68.127

A service like ipinfo.io can then be used for getting the approximate coordinates of the public IP. E.g.

$ curl ipinfo.io/8.8.8.8
{
  "ip": "8.8.8.8",
  "hostname": "dns.google",
  "city": "Mountain View",
  "region": "California",
  "country": "US",
  "loc": "37.3860,-122.0838",
  "org": "AS15169 Google LLC",
  "postal": "94035",
  "timezone": "America/Los_Angeles",
  "readme": "https://ipinfo.io/missingauth"
}

>>Debugging

>>>Logging program output

Get the output of the command:

* * * * * /home/emaus/service_pi_led_function.sh > /home/emaus/crontab.log 2>&1

This might reveal the following:

/home/emaus/service_pi_led_function.sh: 1: /home/emaus/service_pi_led_function.sh: sunwait: not found
/home/emaus/service_pi_led_function.sh: 1: [: =: unexpected operator

>>>Enabling crontab service logging

Enable logging so you can see each time the command is invoked (credits to this SO-answer).

Ensuring the following line is in /etc/rsyslog.conf:

cron.*                         /var/log/cron.log

Then restart rsyslog and cron:

sudo service rsyslog restart
sudo service cron restart

You can then find the logs in /var/log/cron.log.

This file will look something like the following:

Jul 22 22:11:45 Emaus-pi3 cron[13235]: (CRON) INFO (pidfile fd = 3)
Jul 22 22:11:45 Emaus-pi3 cron[13235]: (CRON) INFO (Skipping @reboot jobs -- not system startup)
Jul 22 23:41:01 Emaus-pi3 CRON[17431]: (root) CMD (/home/emaus/service_pi_led_function.sh)
Jul 22 23:41:01 Emaus-pi3 CRON[17427]: (CRON) info (No MTA installed, discarding output)
Jul 22 23:41:47 Emaus-pi3 crontab[16002]: (root) REPLACE (root)
Jul 22 23:41:47 Emaus-pi3 crontab[16002]: (root) END EDIT (root)
Jul 22 23:42:01 Emaus-pi3 cron[13235]: (root) RELOAD (crontabs/root)
Jul 22 23:42:01 Emaus-pi3 CRON[17896]: (root) CMD (/home/emaus/service_pi_led_function.sh > /home/emaus/crontab.log 2>&1)

>Final result

>>Crontab:

# sudo crontab -e

SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

* * * * * /home/emaus/service_pi_led_function.sh

>>Script for setting Raspberry Pi LED function at day/night

# service_pi_led_function.sh

# At day, user regular LED functionality
if [ $(sunwait poll 59.3520323N 50.9725342E) = "DAY" ]; then
    sudo sh -c "echo mmc0 > /sys/class/leds/led0/trigger"
    sudo sh -c "echo input > /sys/class/leds/led1/trigger"
# Turn of LEDs at night so they do not disturb my girlfriend
else
    sudo sh -c "echo gpio > /sys/class/leds/led0/trigger"
    sudo sh -c "echo 0 > /sys/class/leds/led0/brightness"
    sudo sh -c "echo gpio > /sys/class/leds/led1/trigger"
    sudo sh -c "echo 0 > /sys/class/leds/led1/brightness"
fi