Since Dododex hasn't added the raising times I will.
12 hour pregnancy
7 hour 30 minute baby stage
Total maturation time 3 days 3 hours
Total time with pregnancy 3 days 15 hours
Baby reapers eat 6 stacks of cooked meal per hour.
45 stacks should be enough to account for spoilage until it's out of baby stage.
To feed baby reapers easier make an airlocked pen and get a though full of cooked meat in your inventory 5 minutes before it hatches. Use a pheromone gland 3 minutes before birth and then claim it and stay in it's inventory. Force feed it cooked meat as it bites you since biting you makes it lose food. Then once it kills you it should collect all 60 stacks into it's inventory. Use a gland to make sure and if not feed it until gland wears off and stand on your body so the reaper eats the body.
If you put foundations under the reaper it can not burry. This way you can keep farming the same reaper for the best stats because every baby reaper, even if its from the same queen, will have different stats.
To obtain a reaper king you must first find a reaper queen which you must then lower their health to almost dead after you have done this you will have to tank its hits for a while whilst you wait for it to impregnate you once it does this it will bury back underground leaving you at severely low health, at this point you should return to your base where you should have reaper pheramone glands which are obtained by killing reapers however whilst you wait you can gain experience by killing things which will increase the level of your reaper king after it burst, after the 12 hour long wait from first being impregnated is over you should consume a pheramone gland which will alow you to imprint to the baby after it has burst out of you withought killing you, after you have imprinted on it you just raise it much like any other meat eater feeding it raw meat until it matures however if you would like to aquire multiples of these creature you will have to repeat the process ovee again.