public class Import
{
    private static object ImportLock = new object();
    private static DateTime LastImport = DateTime.MinValue;

    public static ImportInfo Import()
    {
        lock (ImportLock)
        {
            if (DateTime.Now.AddSeconds(-10) < LastImport)
            {
                return "no import - time lock";
            }

            LastImport = DateTime.Now;
            return "imported";
        }
    }
}