Most military hospitals in Nigeria take house officers around February. Usually after an intake a new application cycle starts. Applications are simple to make and one does not need to pay for application forms as many hospitals require.The cycle usually ends in November/December when interviews are held in the respective hospitals (Army, Navy and Airforce). They may be held on the same day. Opportunities exist for someone to start at other times but that would mostly be on supernumerary basis with no assurance of remuneration.
Military hospitals usually encourage active participation in the patient management, good hands-on experience and particular attention to discipline and carrying out orders. For those wishing to join the military later this may be more appealing since it gives you an exposure more than a peek from an outsider. Of course, you may not belong to ARD meaning that your pay will be intact (ARD deductions can actually eat in HOs pockets) and you would likely have an accommodation that is mostly furnished, with above-average internet and electricity supply, largely secure and free (some of us paid so much as rent, electricity bills and water bills during housemanship). The first pay may not come immediately but whenever it comes it would be complete with arrears.