I feed layers ad lib all year round and they take more in winter when there is less interesting in the garden, but even the cockerel has it and I've only got one in on growers that isn't POL yet, the other that age is free range now so helps herself to layers too.
They all get corn in the evening, well in the hour before dark which is now about 4pm.. to keep warm and to bring them to a single place for headcounting. Only time in the day you get them all in one place visible at one time!
I wouldn't personally feed speedibeet to hens, but I don't have a scientific reason for saying so. I have it for emergency pony feeding and plain sugar beet too, but it wouldn't occur to me. I'm not sure it would do them any good and I'd rather not take the chance so I'd keep it for sheep if it's a good sheep feed (I don't know sheep feed requirements at all) or otherwise use it only for equines.