The status of cable cars and opening times can be found here:
http://www.discoverpoiana.ro/en/status-teleferice-si-orar/
http://cabanapostavaru.ro/en/skiing-lift-tickets-info/
We arrived in the summer and stayed overnight. At an altitude of 1600 meters there is a guest house Julius Römer Cottage - Postavaru (http://cabanapostavaru.ro/en/), founded in 1883. Very homely and cozy place. The owners are immigrants from Germany.
We left the car on paid parking near the lower cable car station. Took only backpacks, because you have to walk about a kilometer from the top station to the guest house.
There are many bears at the top. They walk around every day, when it gets dark, begging for food. Big dogs live in the guest house to scare them away.
In the evening we climbed to the very top, the weather was excellent. It was a bit scary, since we were alone and afraid of bears :)
Getting there: 20 minutes by car from Brasov. Bus 20 from Livada Poştei in Brasov (N 45 38.741 E 25 35.301). If you arrived by train to Brasov, then take bus 4 and change to bus 20 at the final stop.