Number of days before this event happens (like 'In xx days:'). If Viewer shows today's date and this event happens today, you should see here text 'Today:'. But, if Viewer shows any other date and this event happens on that day, you should see here text 'in 0 days:'. Both 'Today' and 'in 0 days' are displayed with bold font so you can see at first look what are possible alarms for that day.