Get stargazer time with custom cursor

I would like to get the time of a particular stargazer index. (When was this project starred for the 77th time?) To this end, I looked at the GraphQL API. I can get the time of the very last stargaze with

curl -H "Authorization: bearer YOUR_TOKEN" -X POST -d " \
 {\"query\": \"{repository(owner: \\\"zverok\\\", name: \\\"spylls\\\") {stargazers (last: 1) {edges {starredAt}}}}\" \
 } \
" https://api.github.com/graphql
{
  "data":{
    "repository":{
      "stargazers":{
        "edges":[{"starredAt":"2021-03-22T15:25:03Z"}]
      }
    }
  }
}

So that worked, nice. Let’s just add a cursor here: Convert “cursor:77” to base64 and add it as “before”

curl -H "Authorization: bearer YOUR_TOKEN" -X POST -d " \
 {\"query\": \"{repository(owner: \\\"zverok\\\", name: \\\"spylls\\\") {stargazers (last: 1, before: \\\"Y3Vyc29yOjc3\\\") {edges {starredAt}}}}\" \
 } \
" https://api.github.com/graphql
{
  "data":{
    "repository":{
      "stargazers":{
        "edges":[{"starredAt":"2021-03-22T15:25:03Z"}]
      }
    }
  }
}

That seems to have worked, too, cool! But wait, it’s the same time as without the cursor. The cursor seems to have no effect at all. I’m sure the cursor is constructed correctly because if not, you’re getting the response

{
  "data":{
    "repository":{
      "stargazers":{"edges":null}
    }
  },
  "errors":[
    {
      "type":"INVALID_CURSOR_ARGUMENTS",
      "path":["repository","stargazers","edges"],
      "locations":[{"line":1,"column":97}],
      "message":"`Y3VyeHNvcjoxMDA=` does not appear to be a valid cursor."}
  ]
}

Any hint on what might be going wrong here?