I Had A Spontaneous DVT 4 Years Ago And Advised

I had a spontaneous DVT 4 years ago and advised that any flight over 5 hours I would need clexane injections. When flying ling haul 2 years ago I was given 80ml injections - one to be taken an hour before flight and a second one 24 hours later. Am due to do long haul flight again soon and current Dr. Said to have 1 shit an hour before travel and another 24 hours after ARRIVAL. Which is correct?