It can be no longer than 72 hrs from your last departing flight to Canada. So if you have a connection in Chicago to Toronto for example at noon, your 72 hrs would be calculated using the Chicago to Toronto flight. Not departure from MCO.
I went to Walgreens near WDW and did their Rapid ID test, which gives you same day results (I got results in 40 min) so I did my test 48 hrs before departure. It just can’t be more than 72 hrs. They’re strict. I saw someone being turned away at the gate.