You can inject your own properties into solution build.
So you can create your own guid or timestamp in format you need.
Just create file with the name before.[Your solution file name].sln.targets in the folder of your colution.
Here is sample content of this file:
<!--?xml version="1.0" encoding="utf-8"?-->
<Project toolsversion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<MyBuildGuid>$([System.Guid]::NewGuid())</MyBuildGuid>
<MyBuildStartTimestamp>$([System.DateTime]::Now.ToString("yyyyMMdd-HHmmss"))</MyBuildStartTimestamp>
</PropertyGroup>
<Target Name="PrintMyPropertiesdBeforeBuild" BeforeTargets="Build">
<Message Text="MyBuildGuid before build: $(MyBuildGuid)" Importance="high" />
<Message Text="MyBuildStartTimestamp: $(MyBuildStartTimestamp)" Importance="High" />
</Target>
<Target Name="PrintMyPropertiesAfterBuild" AfterTargets="Build">
<Message Text="MyBuildGuid after build $(MyBuildGuid)" Importance="high" />
<Message Text="MyBuildStartTimestamp: $(MyBuildStartTimestamp)" Importance="High" />
</Target>
</Project>