var result = new DateTime(2000, 1, 1);
result = result.AddDays(buildNumber);
result = result.AddSeconds(revision * 2);

<major version>.<minor version>.<build number>.<revision>

<major version>.<minor version>.<build> number>.<revision>

<ItemGroup>
    <RegexTransform Include="$(SolutionRoot)CommonAssemblyInfo.cs">
        <Find>(?<major>d+).(?<minor>d+).d+.(?<revision>d+)</Find>
        <ReplaceWith>$(BUILD_NUMBER)</ReplaceWith>
    </RegexTransform>
</ItemGroup>

msbuild myBuild.proj /p:Configuration="%config%" /p:build_number="%version%"

int revision = (int)time.TimeOfDay.TotalSeconds / 2;

// 24 * 60 * 60 / 2 = 43200 < 65535
Debug.Assert(revision < ushort.MaxValue);

// ...

TimeSpan days = time.Date - new DateTime(2000, 1, 1);
int build = Math.Min(ushort.MaxValue, (int)days.TotalDays);

return new Version(pattern.Major, pattern.Minor, (ushort)build, (ushort)revision);