Why? It's not past day 35, so everything still seems normal now. Rabbits aren't clockworks, when they do what can differ individually and from one time to the next.
I learned to trust my does, but keep checking on her since it can't be long anymore.
If 500g is much depends on their overall weight, and even then I don't think it's much of an issue, I wouldn't try it if the difference is huge (like buck 3 times the does size) or it's very small does like when the dwarf gene makes a doe much smaller than her breed naturally would be without it. But with decent sized rabbits I wouldn't worry about a bigger buck, there's also the viewpoint that the kits size and development is controlled by what the placenta can deliver, and that the fathers genes come mostly into play when growing up.
Nothing to do about it now anyway.
