Getting a bus to anywhere before 0530 isn't easy, as most services don't even start until around 0600.
However the Traveline South West website suggests that he'd have to board the U3 bus at 0243 from Stop E on the campus to Cabot Circus in Bristol.
He's then got a 34 minute wait until Stagecoach South West's FALCON service leaves from stop S4.
That gets to Churchill Gate at Langford at 0412, leaving a 2-minute walk to the ambulance station (and an hour and a quarter wait until 0530 comes around).
That's sourced from here and assumes weekday travel. (I've not checked the weekend times):
https://www.travelinesw.com/
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