Good stuff mate, not many rabbits about daytime nowadays, I used to love ambushing them early morning etc but theres just not the numbers now, good that you have a place you can have a wee run
It shouldn't make any difference if you let your dog hunt up during the day, it'll soon learn when its time to hunt up or not with experience and training,
well done
Go back to basics where its quiet and no distractions if possible, pups maybe got bored with training so make it exciting again, as border bitch said probably lacking something in the diet