It's normal for many fragrant plants. I have a Miltonia Bert Field's 'Eileen' (see my icon above
). It was only fragrant in the morning or evening when it's cool. I have another fragrant orchid, a Bl. Yellow Bird. That was fragrant during night times.
When plants are fragrant, they are working on attracting a type of insect (e.g. bee or fly)... This is part of pollination -- insect goes on flower to get its sap; insect with some pollen from the previous flower goes to another flower to get sap; some pollen is left in the second flower; pollination happens; seeds/seed pods develop.