yep as Lillian says just keep checking any grain once it has turned to seed , it is fairly easy to know when it is ready to cut. You just have to judge ripeness, with the weather for harvesting etc, but again as Lillian says don't cut off the heads/ears of whatever ... but thresh it off. If you cut the heads off , it can be the devils job to get the grain separate . A good effective thresher for smallish amounts is a push bike stood either on a stand or upside down on the saddle and handlebars . You then need one person to turn the pedals so that the back wheel spins, then as it turns just feed the top end of a handful of wheat, whatever, into the spinning wheel very gradually . The spokes will knock off the grains, which should then fall onto a cloth placed under the rear wheel of the bike.
I used this method to do about a ton of wheat and it worked fine. You could fit a small electric motor if you wanted , or even convert an old tumble dryer to do a similar job . Many ways to skin a cat , as they say .
Oats are very easy to grow . Literally sow and they grow . For bunnies you could just cut them when they are ready, tie into bundles/sheaves , and then just hang the sheaves up to feed them to the bunnies . The straw could then be just used as bedding , what they don't eat anyway .
Last April I sowed 6 oat seeds to see if they were viable . They were whole seeds that had escaped the crusher in some rolled oats I had for the horses. I popped them in a pot and they grew....job done, they were viable . So the pot went out side and got left . 3 got eaten by birds or slugs , but the remaining 3 grew well. They continued to grow so I watered them to see how they did . I didn't expect them to go to seed , but they did . Each single seed produced a plant that in turn produced 3 - 4 tillers , these in turn produced a seed head with between 11 and 28 seeds . I will be sowing the small harvest from those 3 seeds this year to see how they do , just for a bit of fun .
cheers
Russ