Here's a simple solution that uses the C# assembly version.

Specify the AssemblyVersion attribute like so:

 using System.Reflection;
 
 [assembly:AssemblyVersion( "1.0.*.*" )]
 
 public class MainMenu : MonoBehaviour {
 ...

And you can retrieve a formatted version number like so:

 print( Assembly.GetExecutingAssembly().GetName().Version.Tostring() );

This prints out the Version in Major.Minor.Build.Revision format (e.g. "1.0.5557.38042"). The Build number is the number of days since Jan. 1, 2000. The Revision number is half the number of seconds since 12:00 AM that day.

If you want, you can use this information to print out a human-readable timestamp (e.g. "3/20/2015 9:08:04 PM"):

 System.Version version = Assembly.GetExecutingAssembly().GetName().Version;
 System.DateTime startDate = new System.DateTime( 2000, 1, 1, 0, 0, 0 );
 System.TimeSpan span = new System.TimeSpan( version.Build, 0, 0, version.Revision * 2 );
 System.DateTime buildDate = startDate.Add( span );
 print( buildDate.ToString() );

This solution was adapted from some other solutions:

• http://xeophin.net/en/blog/2014/05/09/simple-version-numbering-unity3d

• http://forum.unity3d.com/threads/automatic-version-increment-script.144917/#post-992135

You can use a compile-time language to create a string. At least I know that Boo has this.

 import UnityEngine

 

 macro build_buildtime_info():

     dateString = System.DateTime.Now.ToString()

     yield [|

         class BuildtimeInfo:

             static def DateTimeString() as string:

                 return "${$(dateString)}"

     |]

 

 build_buildtime_info

 

 # # Now you can do this:

 # Debug.Log( BuildtimeInfo.DateTimeString() )

Edit:

Unity actually opens every scene during the build process: This can be exploited as follows:

 using UnityEngine;
 
 [ExecuteInEditMode]
 public class RefreshTestCS: MonoBehaviour
 {
     public string buildName;
 
     public void OnGUI() {
         GUILayout.Label("Build name: " + buildName);
     }
 
 #if UNITY_EDITOR
     public void Awake() {
         if (Application.isEditor && !Application.isPlaying) {
             buildName = System.DateTime.Now.ToString() + " (" + (UnityEditor.BuildPipeline.isBuildingPlayer ? "during build)" : "during edit)");
         }
     }
 #endif
 }

EDIT: updated code to make copy of string before returning to C#

Okay here it is:

To be able to show date/time of a build (useful to make sure your testers are using the right version) I made a very simple plugin that adds two functions to retrieve date and time string of the build process. To use it, add the Test.h and Test.mm to the xcode project and JBuildInfo.cs to your unity project. Shouldn't be hard to figure out how to use this I guess...

BuildInfo.h:

// BuildInfo.h

BuildInfo.mm:

// BuildInfo.mm

 char* res = (char*)malloc(strlen(string) + 1);
 strcpy(res, string);
 return res;

 const char* getBuildTime() {
     return MakeStringCopy(__TIME__);
 }   

JBuildInfo.cs:

using UnityEngine; using System.Collections; using System.Runtime.InteropServices;

 [DllImport("__Internal")] private static extern string getBuildDate();
 [DllImport("__Internal")] private static extern string getBuildTime();

 public static string GetBuildDate() {
     if (Application.isEditor) {
         return "<not build>";
     }
     else {
         return getBuildDate();
     }
 }


 public static string GetBuildTime() {
     if (Application.isEditor) {
         return "--:--:--";
     }
     else {
         return getBuildTime();
     }
 }

For iPhone projects, you can use Apple's built-in tool, agvtool, described here. You can probably even use Jaap's answer to provide the generated strings to Unity.