There is nothing to believe, it's all set in canon continuity:
A new hope
0 BBY-0 ABY (where bby is Before Battle of Yavin and aby is After Battle of Yavin)
Empire Strikes Back
Return of the Jedi
: 4 ABY
And on the same site, earliest 'sighting' of the ship in 3 aby and says it would only take 2 - 4 years to finish the entire station.