This doesn't answer your question exactly - but I don't believe that it is possible to do what you need because there isn't a programmatic interface to those drop downs, nor is there a way to manually achieve what you want, so I don't know how having a macro recorder would help
This Website will tell you how to set a meeting up with a custom start time and duration, but you could build your own userform to popup whenever a meeting/appointment is created requesting a start and end time (or start time & duration if you prefer), which is probably the best workaround you'll get.
You could go crazy with this and make a non-modal userform that places itself over the existing controls and replicates their functionality - but that's a lot of coding, and it would be slow because it would be constantly updating its position or hiding itself when the appointment item loses focus, but its very achievable if you are determined.
Outside of VBA/Outlook, you could use Visual Studio to make a VSTO Add-In, creating a new ribbon in the appointment/meeting section, which has two custom controls which modify the start and end dates. You could also populate these with whatever code you want, but you'll probably need to learn C# to do this, although it may be possible with VB.net (which is much more similar to VBA). This Website is a reasonable starting point.
I'm sorry that this isn't really an answer, but I'm afraid that there isn't a satisfactory answer to this question.