unless you have a quick charger that will do a single cell, yes you will have to wait. You want to be sure that nicd batteries get a full charge, especially the first time, as they will develope a memory.
You could always get a D cell ignitor for those times when you want to run but don't want to wait for the charge. It is also good to have one in case your rechargeable fails.
If you want to spend about $50 or more you can buy a peak charger with single cell capability. It will still take a few hours to cycle the D cell battery though. Not 12 hours but a fair amount of time, you don't want to charge it too quickly or you will risk severly decreasing the battery life or burning it up.
OR....you can just do what many of us here have done..... Buy the Hobbico battery and a glow clip (the kind that is used with a starterbox) from TowerHobbies.com or your LHS. I modifued my Glow Clip and added Alligator Clips that you can buy at RadioShack for like .50 cents
this means it would take 9 hours to fully charge this battery from complete discharge.
So check the battery and charger output and just divide the battery/charger output... thats how long you should charge for.