Nowadays, US Visas take incredibly long to get cleared. The time gap between HeroX's shortlisting announcement and time for departure is less than two weeks. Without some sort of push from HeroX to the concerned authorities, it will be impossible - unless the aspirants already have existing visas.
@shyamala Sambasivam Hello, For an in-depth answer to your question please see the Visa Update (link: https://www.herox.com/xprizevisioneers-2018-design-challenge/update/2152) The short answer is that unfortunately, it is unlikely you will be able to secure a Visa in-between the announcement of the winners and Hackathon. As a result, we recommend recruiting to your team someone from a country that does not require a Visa to visit the US. There are threads to help with this at the top of the forum.
Can XPrize give an invitation to people who need to prepone their US visa interview dates. An invitation from XPrize can help in such a case. It need not carry any financial obligation on the part of XPrize. Just an invitation, which the invitee may not exercise in case of not being shortlisted.
My US Visa interview date has been rescheduled to today and now on the way to the consulate. No harm in having a US visa. It normally gets cleared a few days after the interview. The consulate is apparently extremely cooperative in genuine cases and the Global Challenges certainly fall in that category.