There are a number of articles on the internet about Get-Hotfix and date problems.
This seems the best script I have found so far; strangely, I cannot get it to sort on date.
Clear-Host Get-HotFix -ComputerName win7 | where-object {$_.hotfixid -ne "file 1"} | Select hotfixid,description,installedby,@{label="InstalledOn";e={[DateTime]::Parse($_.psbase.properties["installedon"].value,$([System.Globalization.CultureInfo]::GetCultureInfo("en-US")))}}