improve countdown script

scripts/countdown

@@ -16,14 +16,15 @@ function init_day {
 }
 
 if init_day; then
-    next_day=$(($day + 1))
+    next_day=$((day + 1))
     next_timestamp=$(date --date="$(date +%Y-%m)-$next_day" +%s)
     while true; do
-        secs_left=$(($next_timestamp - $(date +%s)))
+        secs_left=$((next_timestamp - $(date +%s)))
         if [ $secs_left -le 0 ]; then
             break
         fi
         printf "\r\x1b[K%s secs left..." "$secs_left"
+        sleep 0.3
     done
     printf "\r\x1b[K"
     init_day