If your tatkal tkt is confirm you can cancel it only on opening date. in such case you will get refund of 25% of base fare. After opening date this tatkal confirm tkt can be cancelled but no refund will be there. If it is w/l you will get full refund only cancellation charges will be deducted. and remaining amount will be transfered into your a/c within 2-3 day from the date of cancellatiion.