hi hun.
i gradually introduce gras from 6 weeks but only sprinkle a few blades in a time each. i know a breeder who put a litter on the grass at 5 weeks old and the whole litter died that night of bloat.
i tell my new owners not to put them on grass straight away but to gradually build up the amount they eat and not before 12 weeks old.

i remove my buns from mum at about 8-10 weeks old but they are giants and should be with mum a bit longer anyway.
not sure what breed you have but some become sexually mature sooner than others.

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I'm sure an hour wouldnt do them any harm unless all their doing is eating the grass

deff split the boys from girls before 12 weeks, If mum looks like shes getting pissed off with them then I guess at 8 - 10 weeks depending on breed

grass can harm them tho, there tums cant always handle greenary

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I know, I had a rabbit as a teen who never ate grass until we got him a friend who showed him how to very weird, so think a little grass is good before they leave I forgot they were so young