I made a few observations in putting together the timeline of events:
Dairy farmer (Henhoeffer) saw smoke plume around 6am on May 7 or 8
Based on the hangar video evidence, it is highly unlikely that the smoke plume was seen on the 7th. The security videos place DM and MS at the hangar from 12:00am to 7:00am that morning, after which they went to Oakville to pick up MM by 8am, and DM was back in Etobicoke by 9am. There is no way they went to the farm and burned the seats around 6am that morning.
On the morning of the 8th, DM's phone pinged in Etobicoke around 3am, but then pinged in Milton at 5:42am and then at the hangar at 7:30am. It is possible that he stopped by the farm within this time to burn the trucks seats, etc. If true, it looks like he did this alone, or at least without the help of MS, since DM spent the rest of the day at the hangar while MS's and MM's phones pinged in Oakville throughout that day.
It is also possible that the burning event took place on the morning of the 9th, but there is really no evidence to suggest that. The cell activity was pretty quiet from the evening of May 8 through the morning of May 9. I am willing to bet that DM caught up on some much needed rest during that time.
Neighbour of farm saw lights at the property around 11:00-11:30pm on May 7 or 8
Based on the evidence, it is possible that the neighbour saw these lights as early as the 6th (the night Tim was murdered). The video evidence suggests DM and MS were picking up the trailer at the farm sometime between 10:30pm to 11:30pm on the 6th before heading to the hangar.
On the 7th, video evidence places DM (or rather, his Yukon) at the hangar from about 9pm to 11:40pm. At 11:40pm the Yukon is seen departing the hangar with the incinerator in tow. Curiously, the Smich/Meneses phone is pinging at the farm property around 11:30pm, suggesting that he was there while DM was at the hangar. How MS got there is unclear. Did DM drop him off there earlier in the evening? Or did he drive there on his own or with someone else (e.g. MM)? Regardless, it is possible that the neighbour saw MS using a flashlight around the farm around 11:30pm. DM would have likely showed up around midnight or later to drop off the incinerator, if he did in fact take it to the farm that night.
On the 8th there is no evidence to suggest DM or MS were at the farm during the evening. As I noted above, the cell activity was quiet that night. I think DM was likely resting up at home in Etobicoke that evening.