Setting is 20 minutes into future - everything is as we know it, or as we can reasonably predict, except the zero-tau capsules.
Capsule is a thin mesh of Unobtanium connected to a portable Handwavium reactor. When turned on, time inside does not flow. Details "by the numbers":
- It is unclear if time inside actually stopped or is just extremely slowed down. A [insert reasonable time here]-long experiment did not show any measurable time inside (in other words, you may adjust this).
- Starting field up and shutting it down can be instantaneous, or take as long as 10 seconds during which time inside slows down or speeds up.
- Field border is sharp, around 1ℓP. We put it in the middle of metal plates that are casing for capsule, to prevent anything from interacting directly with such border (or in near-vacuum between plates, if interactions with metal would be a problem - again this is adjustable).
- Unobtanium mesh is supposed to be something that creates the field, but has no other uses or effects - it does not shield anything from anything, does not get old, nothing. Thus, it shouldn't matter if it's in or out. Probably out, because getting it destroyed would be a good story element, but that's something for another question. Similarly with Handwavium reactor. Please ignore them where possible, their only meaningful effect should be existence of the zero-tau field.
That way, trip to Mars can be as short as 30 seconds, from the passenger point of view.
The problem is: How to safely exit?
Metal walls of the capsule can stop anything bigger than hydrogen atoms, and slow down other things. But that is still around seven months of cosmic radiation, atoms leaking in thorough the seal etc, released in a very, very short time. Sudden gravity change would not help, and probably there are things that I haven't thought of, too.
So, how would we make it safe for our travelers? I want them to survive and I do not want any neural or perception damages. Other than that I can live with, as long as it heals, at least in early stages when we are only setting up Mars operations. We need to get passengers healthy when we go to commercial flights, but if it is too difficult, it can wait.