Generally two to four trial settings are required to meet the target shape and bandwidth. This could take 1-2 hours to complete. It should also be kept in mind that IR dominant systems require an added investment in engineering time to develop custom profiles because of potential problems with shadow effect and color sensitivity of the IR portion of the heating source. Because there is more uniformity of heating in a convection system, one can expect somewhat less time required to develop a solder profile. However, we should note that not all convection systems are created equal.
Some ovens can achieve narrow band width for most products much easier than the others.
There is some misconception, mostly promoted by some suppliers, that if you buy their convection oven, there will be no need for developing a unique profile for each product. Even the same double sided board, depending upon component placement and distribution of copper planes on each side, may require different profiles for each side. And there is also a misconception that if you do need to change a profile, simply change the belt speed. Having to change only the belt speed is certainly easy, but it may not be the right approach. Changing the belt speed changes the temperature of the board in every IR zone.