some do have strong fragrance and some don't. also, i notice that mine are not fragrant until from early evening on into the night. probably has something to do with their pollinators being nocturnal.
n. sylvestris is very fragrant but most of those various colored nicotiana plants (possibly hybridized for color and compact form) i see in garden centers are not fragrant.
which type did you plant?

I have also noticed the fragrance on mine starting at night fall. I swear, as a non scientific person, for some reason I detect more fragrance with this plant on the almost full moon or full moon nights. Maybe I think I do anyway.

I too notice Nicotiana has more scent once the sun sets..and on cloudy days..They're incredible in fall months, too..Which Nic's did you buy? I find the most fragrant are Only the Lonely, which are the tallest of Nic's..I buy seeds and sow directly in the ground..they can grow up to 6' tall, and are really fragrant..
I also notice white flowers are more fragrant than other colors..same goes for white-flowered Petunias..which also thorw out fragrance at night..Toni

Thanks for the responses. I bought the plants from seed and I do not still have the packet...stupid of me. I yanked them out once I knew there was no scent as I am not a fan of their form.