After taking my forehead away from my hands, This reply is for jjd76au
Okay, So... From my training, which is quite scratchy now as this was a few years ago...
Your trip from Kilmore East to City will be covered by your pass as established and as far back out to North Geelong, On Touch off at Geelong, You should be charged the difference outside of your pass, Which should only be a 2 Hour Zone 4.
On boarding the Bus (or Coach) to Portarlington, The 2 Hour should still be active for that location - Once you get to Portarlington and touch off, It should make the adjustment to charge you for a 2 Hour Zone 4-through-5. On the return trip later that day, You should get the same, 2 Hour Zone 4-5.
I could be very very wrong on this, as the requirement that a passenger carry a single valid ticket for an entire journey, may void the above statement. Really, The person who would know, would be Revenue.
I hope my explanation is a bit clearer than the above. (I've avoided going into the mess of explaning Peak and Off-Peak, to keep it simple)