This isn’t currently possible, I’m afraid. There are other playback effects that may depend on various aspects of current state: eg dynamic level, tempo, note length, tremolo rate, etc. We haven’t yet investigated how best to support these, but I envisage that these will be set as properties in each technique combination of the expression map, so you would have three separate “Cresc” entries in the expression map, each with a different duration property, and then Dorico would select the correct one based on the length.
I expect that we’ll also have a means of allowing user-defined playing techniques so that you could manually override the behaviour of each score item, so you’d be able to create ‘pt.my_trombone_cresc.3_seconds’ and attach that to the hairpin. This would give greater flexibility in being to create exactly the effect you want.
You can create your own playing techniques and hide them in the score, and you can disable the effect of the original hairpin, but there isn’t a way make a hairpin automatically play your new technique.
So you can do it, but it’s not going to be an automatic process. You certainly can’t automatically make a hairpin play different ways depending on its duration in seconds.