The dinner doesn't have to take long. The attendant will ask where you are getting off, and I am sure she will ensure a speedy service. Last Friday the dessert was served around Shrewsbury, but I am sure yours can arrive sooner.
Why not make it a few days with the Explore Wales Rovers? The whole Wales one is valid throughout, South Wales version Cardiff to Shrewsbury, and North Wales version Shrewsbury onwards (still entitled to a full meal although reservation is recommended).