How much time needed for a stopover-visit at Longmen Caves?

Hello,

We want to visit the Longmen Caves, and because we're taking a train from Beijing to Xi'an anyway, I thought that it would be the best idea to jump off in Longmen, put our stuff into the Left Luggage area, visit the caves, and take a later train for the final bit to Xi'an.

Can you tell me how much time we have to keep free between the trains if we want to pull this off?
Right now I'd prefer to take the G655 train to Luoyang Longmen (arriving at 14:01), and then take the G837 train at 18:50 to Xi'an. Which would give us almost five hours of time in Luoyang.

Is this too much of a rush? Or will this work out?

Thank you!