2.csproj

<Project>
  <PropertyGroup>
    <AssemblyPath Condition="'$(AssemblyPath)' == ''">PortableTask.dll</AssemblyPath>
  </PropertyGroup>
  <UsingTask TaskName="Sleep" AssemblyFile="$(AssemblyPath)"/>
  <Target Name="t">
    <Message Importance="high" Text="## starting 2 ##"/>
    <Sleep Seconds="3" />
     <Message Importance="high" Text="## finishing 2 ##"/>
  </Target>
</Project>