A nephew had one of these. The parents discovered it pretty much right away, although it didn't pop out much. It continues to get worse and was surgically corrected at 7- 8 months old. He went from being a fussy baby, never wanting to be on his tummy, and slow development, weak neck, etc to a cheerful baby that starting developing rapidly. The surgery went well, a minimum of pain, by the second day he was happier and in less pain than before the surgery, even though he was still healing.
Where is the hernia? lower belly? groin or scrotum?
I think you are right to be concerned. The risk is bowel strangulation where the bowel twists either as it pops out or as it is pushed back in. This can stop circulation and cause that little piece of bowel to die, or at least cause blockage where the bowels can no longer move. My personal opinion is that you do NOT want to wait to get him seen again, hopefully by doctor if the PA is not concerned.