2 weeks. The 1st shot will offer very limited protection, maybe 50%, after 2 weeks.
The 2nd shot will bump it up to the 95%, but I'd again run with giving it 2 weeks after that shot.
Both the Pfizer and Moderna vaccines that are available to Americans require two doses for full protection; a single dose is not as effective as both.
“Early protection against covid-19 may occur from about 12 days after dose one,” said Naor Bar-Zeev*, an infectious diseases physician and epidemiologist at Johns Hopkins Bloomberg School of Public Health. People “should not really consider themselves protected until after a week or two following dose two.”
* Doctor quoted is