If it's the deciduous magnolia with goblet shaped flowers, the latter emerge before the leaves. Once the leaves start to emerge the flowers will start to fade although it's possible to get another flush later in the year. They are beautiful trees and shrubs and and particularly good this year. Yes, the petals do drop as do camellias, rhododendrons and azaleas all prone to being damaged by frost. The petals are a slippery, slimy pain to clear. I know as I worked at an RHS show garden where this was one of my jobs but it's worth it just to see these plants in all their glory.