How to wait a certain amount of time between each execution of a method

All to all,

I have an application that consumes several web services. What this application does that gets many users and creates entries in a .csv file for several projects.

I would like to do the execution for a certain amount of users, every 100 or 200 users the application wait about 30 seconds and continue its execution.

Let this be done until the execution is complete.

I want to avoid loading Querys into the database and prevent the traffic from getting saturated because I make several web calls.

How can I do that?

Thank you very much in advance.

Here is part of my code:

UserData[] userIds = GetUserID();
if (userIds.Length > 0)
{

    List<string> multiUserIDs = new List<string>();

    foreach (var userdata in userIds)
    {
        multiUserIDs.Add(userdata.List[0].ToString());
    }


    string testName = "test_";
    string outCsvFile = string.Format(@"D:\TasksForAllProjects\{0}.csv", testName + DateTime.Now.ToString("_yyyyMMdd HHmms")); 
    String newLine = "";
    var stream = File.CreateText(outCsvFile);

    stream.WriteLine("ProjectName,UserFirstName,UserLastName,TaskStatus);

    string temp = "";

    var AllProjectIds = proj.ProjectID; //Esto viene de otra llamada hecha mas arriba

    string[] projectIDs = new string[] { AllProjectIds }; // all projects
    string singleUserID = "";
    string[] taskStatus = new string[] { "notcompleted" };  

    TaskEntry[] result = GetTasks(projectIDs, singleUserID, multiUserIDs.ToArray(),taskStatus); 

    newLine = string.Format("\"{0}\",\"{1}\",\"{2}\"",
                    item.ProjectTitle,
                    item.UserID,
                    status);
        //Creating a new file when new entries are found.
        stream.WriteLine(newLine);
}
stream.Close();

I see that the problem could come from the variable multiUserIDs which has all the users.

Then I should execute a number of users that comes from that variable.