Wow, that's great. I just googled it to find the answer and Google said 30 days. I guess in real life they're a little more flexible than the official policy!
"May I transfer my voyage to my travel agent?
Yes, Virgin Voyages will gladly transfer a reservation to your travel agent within 30 days from the creation date when a reservation is not paid in full."
https://www.virginvoyages.com/help-and-support/before-you-sail/new-bookings#:~:text=May I transfer,paid in full.