The ramp time is controlled by two config parameters: 7, aka Z-Wave Command Dim Step, and 8, aka Z-Wave Command Dim Rate. 7 is described as:
Indicates how many levels the dimmer will change for each dimming step.
And 8 is described as:
This value indicates in 10 millisecond resolution, how often the dim level will change. For example, if you set this parameter to 1, then every 10ms the dim level will change. If you set it to 255, then every 2.55 seconds the dim level will change.
Z-Wave levels go from 0 (off) to 99 (full on.) The default for 7 is 1, and the default for 8 is 3. So, it takes 99 steps (99 levels / 1 level per step), and each step is 30 ms (3 x 10ms), so 99 x 30ms = 2.97s.
FWIW, I have two different versions of the GE/Jasco plug-in dimmer, and for both I set delay to 3 and it works fine.