It is. You got off lucky. It took me 10s of hours over two months to book some VN flights before. Countless calls until a non-clueless agent knew what they were doing (DL doesn't believe in training its staff, or in QA), but then couldn't get VN even over long-sell and had to do some very convolluted manual process even more backwards than long-sell. Took a good two months to get the seats confirmed and ticketed and 10-20 hours in the whole process.

Generally, thougn, expect the ordeal of booking a 006 ticket to take about as lon gas the flying time of your flights (with the numerous escalations and often 3, 4, 5 agents all on at once trying to do routine things that with other airlines you can do online, such as booking flights, making required changes due to schedule changes/cancellations even of DL's own flights, etc.). If it's any less time than that, then you are very lucky!