if your on a TR visa then you do not need to have outbound flight confirmation. I came in on friday without it and was not questioned at all. On my T6 i put 60-90 days of duration of stay,
I just arrived Friday and I was not even questioned about a return ticket (I don’t have one as I’m going to try and chance my visa here to something longer)
The results must be issued within the 72 hour period prior to your flight. along with a Fit to Fly certificate. The actual test can be taken outside the 72 hour window, which in some countries is advisable because the results take time to process. If you can find a lab that can produce in 24-48 hours that is your best option. get the test the 4 days before the flight, you should have your results within the 72 hour period. go see a dr within the 3 days of your flight to get the F2F certificate.
Its really not that hard to understand. You just have to know how long results take in your country/city. Call the places that do the testing to see how long their results are taking, and figure out when to get tested from there..