Had anyone told Peter and John to stop going to the temple at the prayer hour in Acts 3?
No such command had been given. Peter and John kept going to the temple at the stipulated prayer hour, the ninth hour, because they were still following the Jewish habit and ritual of temple prayer. No one had instructed them otherwise.
Les explains that no one had told them not to go to the temple. Not only did they go, but they went on a required hour, showing that this practice was still stipulated for them. He contrasts this with the grace age, where believers are not commanded to meet at the church house for prayer at a particular hour, though Mohammedans do have set hours of prayer. These men were still under the Jewish habit and ritual of going up to the temple at the ninth hour, since it was the hour of prayer. Les then notes the next amazing thing: as they went to the temple, a lame man was there, carried daily and laid at the gate called Beautiful to ask alms. He points out that the Lord Himself must have passed this begging man off and on for three years, yet did not heal him, because the sovereign God does everything with a purpose. He compares this to Lazarus, where Jesus purposely delayed so Lazarus would die and then be raised.