http://powershell.org/wp/forums/topic/need-to-rename-files-by-date-and-time/#post-29394

powershellorg-forum-post-29394-reply1.ps1

Param
(
    [Parameter(Mandatory)]
    [System.String]
    $Path,

    [System.String]
    $Filter = '*.jpg',

    [System.String]
    $NewNameFormat = 'DSC_{0:d3}.jpg'
)

[IO.FileInfo[]]$Files = Get-ChildItem -Path $Path -Filter $Filter -File | 
    Sort-Object -Property LastWriteTime

for ($i = 0; $i -lt $Files.Count; $i++)
{
    $NewName = $NewNameFormat -f ($i + 1)
    
    # Remove -WhatIf if you want files to actually be renamed
    Rename-Item -Path $Files[$i].FullName -NewName $NewName -WhatIf 
}