Minutes. I guess it depends on the lenght of the tunnel, but it's something like 10 minutes or so.
Another time-related question is how time itself would act in another space. Time, of course, is relative. Psychological time, the time all people realises, is really just a byproduct of thermodynamic time, calculated by the amount of disorder in the universe and in the world. Your body transforms food into energy, thus adding to the disorder.
So, how would this time react in another universe? If there is no matter, there is no order, thus there is no time. The spaceship itself is a closed enviroment, and the disorder increases inside it, but what about the surrounding enviroment? What if time travels faster inside subspace? Or slower? Maybe it doesn't exist, and only temporarily comes to being when an object with matter passes through subspace. What if the Shivans for some reason want to keep the space totally organised (they're like über-Vorlons on a totally massive scale), and want to destroy everyone that would increase the disorder by bringing matter into it.