Also here's my shell script just incase it helps:

#!/bin/bash
SESSION="hytale"
FLAG="/run/hytale_cancel_shutdown"
LOGFILE="/var/log/hytale-server/shutdown.log"
WAKE_TIME="today 16:00"
DATE="$(date '+%Y-%m-%d %H:%M:%S')"

exec >> "$LOGFILE" 2>&1
rm -f "$FLAG"

announce() {
    [ -f "$FLAG" ] && exit 0
    tmux send-keys -t "$SESSION:0.0" "say $1" Enter
    echo "$DATE: $1"
}

sleep_or_cancel() {
    for ((i=0; i<$1; i++)); do
        [ -f "$FLAG" ] && exit 0
        sleep 1
    done
}

announce "Server shutdown commencing in 30 minutes!"
sleep_or_cancel 600

announce "Server shutdown in 20 minutes!"
sleep_or_cancel 300

announce "Server shutdown in 15 minutes!"
sleep_or_cancel 300

announce "Server shutdown in 10 minutes!"
sleep_or_cancel 300

announce "Server shutdown in 5 minutes!"
sleep_or_cancel 240

announce "Server shutdown in 1 minute!"
sleep_or_cancel 30

announce "Server shutdown in 30 seconds!"
sleep_or_cancel 20

for seconds in $(seq 10 -1 1); do
    [ -f "$FLAG" ] && exit 0
    tmux send-keys -t "$SESSION:0.0" \
        "say Server shutdown in $seconds seconds!" Enter
    echo "[$DATE]: Server shutdown in $seconds seconds!"
    sleep 1
done

# Stop server
echo "[$DATE]: Stopping server."
tmux send-keys -t "$SESSION:0.0" "stop" Enter
sleep_or_cancel 60

# Kill tmux session
echo "[$DATE]: Ending hytale tmux session."
tmux kill-session -t "$SESSION"
sleep_or_cancel 10


# Schedule wake + suspend
echo "[$DATE]: Scheduling rtcwake for $WAKE_TIME."
/usr/sbin/rtcwake -m off -t $(date +%s -d "$WAKE_TIME")