I agree! And that is likely the motorcycle currently being forensically analyzed, IMO.
If LE can get that level of detailed imagery on that particular moment in time, the subliminal message sent to the suspect(s) could be, 'We have this imagery for any day or night we care to analyze.'
Additionally, me thinks motorcycle head lights could be picked up at night by what I presume is sophisticated satellite imagery. A single head light anywhere on the two properties SM and JM care for, around the time Gus was reported missing, could be telling and may lead to Gus.
ETA: clarifying words
Human nature being what it is, I would be extremely surprised if Gus wasn't "removed" from the property before 5pm.
The reason to concoct a story to explain his disappearance, is largely based around providing alibis to the person/s involved. You risk losing control of the situation if you wait until after the "sandpit story" to dispose of the body. I think it is highly unlikely he was driven anywhere after dark.
I do think the motorcycle is relevant in LE eyes and it is no coincidence it has been highlighted in the presser, as well as being seized.
In trying to work out which grandparent is responsible, I find it harder to make a case for Shannon on her own. If Josie and Jess were both 10km away tending to sheep
the whole time, then where would the discrepancy in statements come from? Josie and Jess would be able to 100% verify each other's movements. Shannon could basically say anything, because no-one could refute it or provide conflicting details - either at the time, or in subsequent statements down the track. Slight changes in time could easily be put down to stress-related memory issues.
Using that logic, and given Jess has been excluded, that only leaves one person's statement under question. That really has to mean that Josie and Jess weren't together all day. The obvious discrepancy would be based around what time Josie joined Jess, probably using the motorbike.
Something likely happened to Gus after Jess had left. Impossible to know exactly who did what, but very likely both granny's were aware. Story concocted. Probably Josie takes the body somewhere before joining Jess. The likely discrepancy is the missing time between departure from the homestead (Shannon's version) and arrival at the sheep tending (Jess' statement). Over time, at least one granny via subsequent statement/s, has created a situation whereby a 20 minute bike ride appears to have taken significantly longer IMO.