Is sprint 0 time-boxed?
Logically it does not seem like it is, but some people claim it should be? So, is it formally a time-boxed event?
there is nothing such as a "Sprint 0". The very nature of a Sprint is that it is timeboxed to not more than 30 days and that it delivers a potentially shippable product increment. If you conduct a "Sprint 0" as some sort of non-timeboxed thing to produce something of 0 value (like sketching the architecture), you are not doing Scrum even though you might use the vocabulary.
If you have to do some sort of "project preparation", call it just that. If you want to save hussle and money, timebox it to 2 weeks, never more than 4 weeks. Anything else is a waste of precious energy and resources.
Question exam preparation and manual response.
As Dominik says, in Scrum there is no recognition of Sprint Zero. In practice the term tends to be used for early Sprints that never find their stride, or for which Scrum components like a Product Backlog, Scrum Master, or Product Owner have not yet been secured.
A Sprint Zero is usually seen retrospectively. Few teams plan to have one, so it is rarely time-boxed. A simple, WIP limited Kanban of project set-up tasks is often better than trying (and failing) to use Scrum in a precocious manner.
Can you please elaborate what you do during this so called Sprint-0 and why do you think it exists?
I feel this is mainly derived by PMs for development of integrated components. They try to do the traditional design part as part of sprint 0 specially when they have multiple component integrations, external vendors involved etc
I have also seen this is the time they try to get the resources on board (hardware and people), trainings, KT etc.
But as Dominic pointed out its the "project preparation" and can be time boxed for 2 weeks