$initialDate = [datetime]'2013/1/8'

$rollingDate = $initialDate

do {
    $client = New-Object System.Net.WebClient
    $results = $client.DownloadString("http://not.a.real.url")
    Write-Host "$rollingDate.ToShortDateString() - $results"
    $rollingDate = $rollingDate.AddDays(21)
    $username = [System.Environment]::UserName
} until ($rollingDate -ge [datetime]'2013/12/31')