Count commits to a specific owner's repository for a specific time period.

GitHubCommitCounter.cs

using Newtonsoft.Json.Linq;
using System;
using System.Net.Http;
using System.Linq;
using System.Threading.Tasks;

public static class GitHubCommitCounter
{
    public static async Task Count(string owner, DateTime minDateTime)
    {
        using (var httpClient = new HttpClient())
        {
            httpClient.DefaultRequestHeaders.Add("User-Agent", "C# HttpClient");

            var repositories =
                JArray
                    .Parse(await httpClient.GetStringAsync($"https://api.github.com/users/{owner}/repos"))
                    .Select(x => (string)x["name"]);

            foreach (var repository in repositories)
            {
                var json = await httpClient.GetStringAsync($"https://api.github.com/repos/{owner}/{repository}/commits");
                var count = JArray.Parse(json)
                    .Where(x => (string)x.SelectToken("author.login") == owner
                            && minDateTime < DateTime.Parse((string)x.SelectToken("commit.author.date")))
                            .Count();
                if (0 < count)
                    Console.WriteLine($"{repository}:{count}");
            }
        }

    }
}