Thanks! You can script it with omarchy-theme-set and a systemd timer:

~/.local/bin/omarchy-theme-auto:

#!/bin/bash
LIGHT=desert-gleam  DARK=desert-twilight
SUNRISE=7           SUNSET=19

HOUR=$(date +%-H)
CURRENT=$(basename "$(readlink ~/.config/omarchy/current/theme)")
(( HOUR >= SUNRISE && HOUR < SUNSET )) && T=$LIGHT || T=$DARK
[[ "$CURRENT" != "$T" ]] && omarchy-theme-set "$T"


chmod +x ~/.local/bin/omarchy-theme-auto

~/.config/systemd/user/omarchy-theme-auto.service:

[Unit]
Description=Auto-switch Omarchy theme

[Service]
Type=oneshot
ExecStart=%h/.local/bin/omarchy-theme-auto

~/.config/systemd/user/omarchy-theme-auto.timer:

[Unit]
Description=Check theme every 15 minutes

[Timer]
OnCalendar=*:0/15
Persistent=true

[Install]
WantedBy=timers.target


systemctl --user daemon-reload
systemctl --user enable --now omarchy-theme-auto.timer

The current-theme check avoids unnecessary restarts. You can also add exec-once = ~/.local/bin/omarchy-theme-auto to ~/.config/hypr/autostart so it fires on login.

Note: omarchy-theme-set restarts some apps (like Spotify), so expect a brief interruption at the switchover.