I have no information on germination of E mirabilis but it grows in hot dry places at about 1000-1500m elevation. It often grows in bright light beneath sparse foliage of widely spaced, often deciduous trees. It can also grow on cliffs or in thick duff on rocks. It flowers during the dry season when it is usually (maybe always?) leafless. The dry season is very dry but there may be occasional light or heavy rains.
Lou