Timing

There are three ways you can do this: VBA.Timer, GetTickCount API or timeGetTime API.

VBA.Timer

This returns the number of seconds elapsed since midnight using a single-precision floating point value.
This is not a threaded control so may not be triggered at exactly the correct time.
Delays can be caused by other applications and or system processes.

Public starttime As Single 
Public timeelapsed As Single 

Public Sub RunCode() 
Dim l As Long 
Dim a As Long 
    For l = 1 To 800000000 
        a = a + 1 
    Next 
End Sub 

Public Sub Timer1() 
    starttime = VBA.Timer 
    Call RunCode 
    timeelapsed = VBA.Timer - starttime 
    'Call MsgBox(timeelapsed & " seconds")
    Call MsgBox(Format(timeelapsed / 60, "##0.###") & " minutes") 
End Sub 

GetTickCount API

This returns the number of milliseconds that have elapsed since Windows was started.
This will run for 49 days before resetting back to zero.

Public Declare PtrSafe Function GetTickCount Lib "kernel32.dll" () As Long 

Public Sub Timer2() 
    starttime = GetTickCount() 
    Call RunCode 
    timeelapsed = (GetTickCount() - starttime) 
    Call MsgBox(timeelapsed / 1000 & " seconds") 
    Call MsgBox(timeelapsed / 60000 & " minutes") 
    Call MsgBox(timeelapsed / 3600000 & " hours") 
End Sub 

timeGetTime API

This returns the number of milliseconds that have elapsed since Windows was started.

Public Declare PtrSafe Function timeGetTime Lib "winmm.dll" () As Long 

Public Sub Timer3() 
    starttime = timeGetTime() 
    Call RunCode 
    timeelapsed = (timeGetTime() - starttime) 
    Call MsgBox(timeelapsed & " seconds") 
End Sub 

Finding Bottlenecks

link - msdn.microsoft.com/en-us/library/aa730921