When do the candle-buds that Simon sees bloom

This is when the boys are travelling to explore the island to see if it is in fact an island.

They bloom at sunset;

"Simon dropped the screen of leaves back into place. The slope of the bars of honey-colored sunlight decreased; they slid up the bushes, passed over the green candle-like buds, moved toward the canopy, and darkness thickened under the trees. With the fading of the light the riotous colors died and the heat and urgency cooled away. The candle-buds stirred. Their green sepals drew back a little and the white tips of the flowers rose

delicately to meet the open air. Now the sunlight had lifted clear of the open space and withdrawn from the sky. Darkness poured out, submerging the ways between the trees till they were dim and strange as the bottom of the sea. The candle-buds

opened their wide white flowers glimmering under the light that pricked down from the first stars. Their scent spilled out into the air and took possession of the island."