Has it been stated anywhere how long his vacation is for now?
I think it's been pretty standard for most of our high profile transfers the last years to have our negotiation team and the selling club hash out details with the assistance of the players agent. If the two clubs agree, the agent will likely inform the player of his options while he is still on vacation, but nobody expects him to make a full decision before his vacation is over. Let him mull it over. Or even if he does make a decision, nothing is expected to move further before the vacation is over and next steps like final details on personal terms, medical and so on can be completed.
As much as we muppets would like it, we don't ask high profile players to cut their vacations short. Thus no official bids until then either, but likely we'll have agreed all the deal terms before then.
Dortmund is doing a digital pre-season "tour" for China this year, letting fans view livestreams of their trainings back in Dortmund with Chinese commentary, digital meet and greet with players etc, not sure when it starts? Bayern's similar thing started 25th of July and ends August 2nd.
If the clubs are close I doubt Dortmund would want Sancho to partake in this online stuff.