Refresh-frequency-calculation's start date for a full sandbox

Question

This will take me 29 days to test, hence asking the following question.

Context: You can refresh a Full sandbox every 29 days.

Question: Will I be able to see the refresh hyperlink for a full sandbox:

1. 28 days after clicking Refresh, or
2. 28 days after receiving the Refresh Complete email, or
3. 28 days after clicking Activate, or
4. 28 days after receiving the Activation Complete email?

Answer 1

The correct answer is 2.

The 29 days will be calculated from the day the you receive the refresh complete email.

Source: Salesforce Premier+ Support.