Oh, finally! I passed this mission after ca. 30 bad tries. A week ago I was very upset , found this guide and decided to pass the mission in Staunton, but there was a problem: I do not know Staunton at all. And that meant I must firstly discover it. Plenty of time! That is why I’ve kept trying in Portland. And I've done it! And once again .
The key was - NOT to try to pick up patients in groups of three at any cost. Better to be more flexible. Group of 3 is the best variant. But it’s also okay to take only 2 patients at one time and take them to the hospital, if they are near to each other but quite a distance from other patients.
25 sec for one plus 25 sec for the second = ca 1 minute limit or even more. Enough to return to the Hospital, set out both patients and then reach the next patient. The alone standing patients can be the cause of failure, because you get only 25 sec bonus time for him or her. Only just to reach Hospital. But no more time to pick up the next group of patients after the hospital. So if there are for example 12 patients, who stand in groups of two, it is sometimes better to make 6 trips instead of 4, and so you will have enough time for carefully driving and even small mistakes.