Set user default regional settings from website default

$spweb = Get-SPWeb http://yourURL.com
$user = get-spuser -Web $spweb -Identity "DOMAIN\USER"
$reg = $user.RegionalSettings
$newReg = new-object Microsoft.SharePoint.SPRegionalSettings($spweb);
$user.RegionalSettings = $newReg;
$user.Update();

Powershell script activate developer dashboard on demand in your Sharepoint 2013 environment

$svc = [Microsoft.SharePoint.Administration.SPWebService]::ContentService
$dds = $svc.DeveloperDashboardSettings
$dds.DisplayLevel = "OnDemand"
$dds.TraceEnabled = $true;
$dds.Update()