World champion Lewis Hamilton posted the fastest time in both sessions, while Red Bull's Max Verstappen was second in both.
Yesterday's times still don't give a true indication of where each car is at with different tyres and fuel loads being spread throughout the field.
It meant that there were few opportunities to make direct comparisons between cars.
Hartley also completed his first competitive laps outside the winter tests with the new halo safety feature fitted to his Toro Rosso car.
Drivers and pundits have complained about the aesthetics being affected by its introduction, while it also obstructs the amount of vision drivers can see from within the car.
Having spent plenty of time in the cockpit of the Porsche LMP1 car in the World Endurance Championship, he has some experience with a limited field of vision.
"From the outside, it is not very visually pleasing," Hartley said. "Luckily when you are sitting in the car, you don't see it - we actually look through it, so from my perspective, it is invisible.
"It is a bit tricky to get in and out of the car, but it is there for a reason. It is there to protect our heads.
"There have been fatalities in the past and in other formulas from flying objects.
"We know why it is there. Like any rule change in Formula 1, it takes a while to get used to it, but already now after testing, it starts to become almost normal to see it there."
Hartley will take part in another practice session this morning before qualifying later in the day.
