kitten has a lump. hernia?

[Silbury]

Just felt it when i picked him up. On his tum. Then it was gone again. The felt it again.

Is it safe to ignore overnight?

I would say so, bit late I am afraid.
I had a girl cat who'd had a litter of kittens. She had a hernia which poked out then went back in.
When I had her spayed, they did a midline incision and solved two problems with one swipe of the scalpel.
HTH.

Crikey, just re read and it is him. Same advice, go to the vet. She will be able to advise you.