Translation:The tourists were exiting the train for five or six minutes.
is it meant that the act of getting off the train took five to six minutes?
Should allow exiting "from" the train. US English often omits words like this, whereas UK English requires them. Another example is where in the US, you protest something, but in UK English you must us protest "for" or "against". It's also marked as transitive/intransitive too. So, as an intransitive verb, you must use "from".
I have added alternatives that include "from," as Oxford Living Dictionaries supports it: https://en.oxforddictionaries.com/definition/exit. Sample sentence similar to the one in this exercise: "‘While I was waiting at the arrivals gate, a large group of people exited from the flight previous to the one I was waiting for.’"