A.T. Robertson Commentary Acts 3:1

"Now Peter and John were going up into the temple at the hour of prayer, [being] the ninth [hour]." — Acts 3:1 (ASV)

Were going up (ανεβαινον). Descriptive imperfect active. They were ascending the terraces to the temple courts.

The ninth (την ενατην). Our three o'clock in the afternoon, the time of the evening sacrifice. Peter and John like Paul later kept up the Jewish worship, but not as a means of sacramental redemption. There were three hours of prayer (third, sixth, ninth).