These are some cron alternatives for waking a user/reminding him of Prayer 15 minutes before the Azan. The time is based on Asia/Karachi timezone. You can always edit the time by editing the related timer files.
Copy required files in ~/.config/systemd/user/:
git clone https://gitlab.com/Abdullah/prayer-timers.git
mkdir -p ~/.config/systemd/user/
mkdir -p ~/.local/share/misc/
cd prayer-timers
cp *.timer ~/.config/systemd/user/
cp *.service ~/.config/systemd/user/
cp Kursi.ogg ~/.local/share/misc/
systemctl --user daemon-reload
# You can now invoke this to activate all timers.
systemctl enable --now {fajr,zuhr,asr,maghrib,isha}.timer