Your Nagpur Duronto rake has arrived CST @ 6am in the mmorning along with a dozen more trains. So the Maintenance line will be busy.
Hence the confusion.
Regarding...
more... Tatkal tickets, when trains are more than 3 hours late from originating stations, full refunds are pernissible. You can contact the Help desk at CST for more details.
Thanks and have a safe journey.