https://github.com/grke/burp/issues/627

Index: configs/server/timer_script
--- configs/server/timer_script.orig
+++ configs/server/timer_script
@@ -77,29 +77,12 @@ get_intervals()
 
 	read junk ts < "$timestamp"
 
-	if   ! secs=$(LANG=C LC_TIME=C date +%s -d "$ts") \
-	  || ! now=$(LANG=C LC_TIME=C date +"%Y-%m-%d %H:%M:%S") \
-	  || ! nowsecs=$(LANG=C LC_TIME=C date +%s -d "$now")
-	then
-		echo "$0: Date command returned error for $client."
-		return 0
-	fi
-
+	mts=$(echo $ts | sed -e 's/-//g; s/ //; s/://; s/:/./')
+	secs=$(LANG=C LC_TIME=C date -j "$mts" +%s)
+	now=$(LANG=C LC_TIME=C date +"%Y-%m-%d %H:%M:%S")
+	nowsecs=$(LANG=C LC_TIME=C date +%s)
 	min_timesecs=$((secs+intervalsecs))
-
-	# GNU coreutils 'date' command should accept the following (even
-	# slightly old versions).
-	if ! min_time=$(LANG=C LC_TIME=C date -d "Jan 1, 1970 00:00:00 +0000 + $min_timesecs seconds" +"%Y-%m-%d %H:%M:%S")
-	then
-		# FreeBSD 'date' will return an error with the above, so try
-		# a version that FreeBSD 'date' should be happy with.
-		if ! min_time=$(LANG=C LC_TIME=C date -r $min_timesecs +"%Y-%m-%d %H:%M:%S")
-		then
-			echo "$0: Date command returned error for $client."
-			return 0
-		fi
-	fi
-
+	min_time=$(LANG=C LC_TIME=C date -r $min_timesecs +"%Y-%m-%d %H:%M:%S")
 	echo "Last backup: $ts"
 	echo "Next after : $min_time (interval $interval)"