GitHub: extract the date of the last activity of the GitHub user

please help me: how can I extract the date of the last activity of the GitHub user?

GHRepository repository = service.getGitHubRepository();
List<GHPullRequest> pullRequests = repository.getPullRequests(GHIssueState.ALL);

for (GHPullRequest pr : pullRequests) {
    if (pr.getCreatedAt().after(startDate)) {
        names.add(pr.getUser().getLogin());
    }
}

this method is very slow and imperfect