Powershell script to get Sleep, Wake, Shutdown, Restart, Wireless/Wired Connection & Disconnect Events from the Eventlog. I will clean this up in the future, but wanted to record it quickly for the moment.

Get-OfflineEvents.ps1

param( $Newest = 10 )

function Parse-EventLogEntry
{
    param(
        [Parameter(Mandatory=$true, Position=0, ValueFromPipeline=$true)]
        [System.Diagnostics.EventLogEntry[]]
        $eventInfo
    )

    Process
    {
        foreach ($info in $eventInfo)
        {
            $enterSleep = [DateTime]::Parse($info.ReplacementStrings[0]);
            $exitSleep = [DateTime]::Parse($info.ReplacementStrings[1]);
            $duration = $exitSleep - $enterSleep
            $wakeSource = 'Unknown'
            if ($info.Message -match 'Wake Source:\s*(.*)$')
            {
                $wakeSource = $matches[1]
            }
            new-object psobject -Property @{Duration = $duration; Sleep = $enterSleep; 
                                            Wake = $exitSleep; WakeSource = $wakeSource}
        }
    }
}

# Sleep/Wake Events
Get-EventLog -LogName System -Source Microsoft-Windows-Power-Troubleshooter -Newest $Newest -ErrorAction SilentlyContinue  | Sort TimeGenerated | Parse-EventLogEntry

# Shutdown/Restart Events
Get-EventLog -Logname System -Newest $Newest -Source "USER32" | Select TimeGenerated,Message

# General NIC Events
Get-WinEvent -FilterHashtable @{ProviderName='Microsoft-Windows-NetworkProfile'; id=10000,10001} -MaxEvents $Newest | Select TimeCreated,Message

# Wireless Connection Events
Get-WinEvent -FilterHashtable @{ProviderName='Microsoft-Windows-WLAN-AutoConfig';} -MaxEvents $Newest | Select TimeCreated,Message