this is the first of our Oncidiums to rebloom with the others following him. the flowers all opened within a few days. but no fragrance yet after a couple days. I know he smells good as we bought it in bloom. does it take a bit for them to start smelling?
Yes. It can. And different environmental conditions can affect the strength. Get it into some bright natural light (not full sun), make sure the temps are reasonable, and that the humidity isn't low. Also, move it away from breezes and drafts.
Scent also depends on time of day. Most oncidiums I've had had the strongest scent in the morning, tapering out during the day until it was nearly or wholly faded in the evening/night. Two plants so far have been exceptions to that, with one fragrant at night but not at all during the day (so I hadn't even noticed initially) and one fragrant throughout day and night. My miltoniopsis did not start really throwing out fragrance until its blooms were open for nearly two weeks though that might have been something environmentally.
Try sniffing your flowers at different times?
I am very curious what it smells like. Orchid fragrance is more varied than any other flower I have grown or known.