It is well documented in the pre-order FAQ that the Joined Trill is the only perk that is not retroactive. Knowing I am going to have more than one character in the future anyway, I started a liberated Borg Tac and a Human Eng during head start. I can wait for my Joined Trill doctor until 2/2 so head start is not a waste.
I plan to make a joined trill engineer, but honestly waiting until Tues is hardly a huge deal. I'm having a good time playing my vulcan science toon and borg tactical one. Remember the impacts of the joined trill will start to fade a bit as you level further and further. No company makes one race you select at start overpowering. The Borg you get for lifetimes subs are not and the joined trill won't be either.