It can take quite a few weeks to do stairs normally--especially down. It's really trial and error to see what is too much.
With my first knee, the PT pushing me to do things I wasn't ready for (such as squats) gave me a nasty case of quad tendonitis. That takes a while to get rid of. The PT with my second knee encouraged me to try my limits, but also didn't push me to do things I wasn't ready for. No tendonitis and less pain in recovery, with a result as good or better than the first knee.
With my first knee, the PT pushing me to do things I wasn't ready for (such as squats) gave me a nasty case of quad tendonitis. That takes a while to get rid of. The PT with my second knee encouraged me to try my limits, but also didn't push me to do things I wasn't ready for. No tendonitis and less pain in recovery, with a result as good or better than the first knee.