The Finn insisted the team and himself were still in discovery mode as the W08's potential is gradually unveiled.
"We managed to complete more mileage - more than 80 laps in four hours - which is good," Bottas said.
"We're still focusing on the long runs and doing setup changes and learning about the car, so it was a valuable day."
Echoing Lewis Hamilton's comments after the morning session, Bottas admitted the team was not yet satisfied with the car's status.
"We haven't quite got to the point where we want to be yet. There's always work to do with the car and we're evaluating all the upgrades - what's good and what's not good - and seeing in what areas we still need to improve.
"We're not looking at lap times right now, but we can beat the 1:19.705 we set last week if we want to, it's definitely possible."
Asked to cast an opinion of Mercedes' rivals, Bottas was another driver to note the impressive pace of the cars in red.
"I think Ferrari are looking very good - they seem to be consistent and fast. We shouldn't underestimate them or Red Bull.
"We'll need to keep working hard to be in the best shape possible for Melbourne."