The LZW42 does support ramp rate/transition times, but it is up to your hub or controlling device to specify the transition time when issuing an on or off command.
I tested this by turning on a bulb 3 different times, once using the default transition (4-5 seconds), once using a 10 second transition, and once with an instant transition, and everything worked as expected.
I do think it would be nice to have a config parameter for the default dimming duration though. It would help in situations where the hub or controlling device does not allow you to specify a duration.