MSBuild how to get a good formatted date

msbuild-get-date.proj

<Project 
  xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
  ToolsVersion="4.0"
  DefaultTargets="Demo" >

  <Target Name="Demo">
    <PropertyGroup>
      <CurrentDate>$([System.DateTime]::Now.ToString(yyyyMMdd-mmss))</CurrentDate>
    </PropertyGroup>

    <Message Text="CurrentDate: $(CurrentDate)"/>
  </Target>

</Project>