What is the meaning of S+4

I assume this has been covered before, but I looked and haven’t found an answer.

S+4 with NU7Y (Posted by WU7H)

what does the “S+4” mean?

It’s a designator which will extend the normal spotting period of RBNHole +4 hrs later than the standard period it spots.

More info on RBNHole and its usage can be found here: RBNHole | VK3ARR's SOTA Blog

Thanks Joe