STOP HERE for a moment ...... Here's a decision point. If you know what times you want to input, skip from here to the section below labelled "Altering the Arrival and Departure Times".
If you want to let MSTS set the times for you, press "Recalculate this" and a series of arrival and departure times appear.

So far so good....... you think.
When you try out the activity, you find that the times are just not accurate or realistic.
How can you change the times to reflect a more accurate timetable? It can be done in MSTS' Activity Editor quite easily..... but not intuitively (but you know that about MSTS by now anyway).
You can do this in two ways, either by referring to the prototypical timetable (public or employee) or by running a train over the route and measuring the running times between stations.
For this tutorial, I'm using arrival/departure times based on figures that Gary O'Connor came up with after running a consist on the Australian Central West route (v1.6):
Town Arrival Departure
Cullya 10:12 10:13
Mullion Creek 10:16 10:17
Kerrs Creek 10:31 10:32
Warnecliff 10:43 10:44
Euchareena 10:48 10:49
Stuart Town 11:05 11:06
Mumbil 11:12 11:13
Dripstone 11:20 11:21
Wellington 11:28 11:29
Maryvale 11:33 11:34
Guerie 11:45 11:46
Wongarbon 11:52 11:53
Eulomogo 11:59 12:00
Dubbo 12:10
Open the activity in Activity Editor (AE). On the "Player" screen, click on "Edit Timetable" (see arrow #1 below). A timetable (initially with all starting times the same) will pop up.

If you click on "Recalculate This" (arrow 3 below), you get a series of times selected by the AE:

Don't!!!
If you try to run a train based on these times you may find that the operation is not very realistic.