Hi,
How are you? An allergic reaction indeed may occur immediately after exposure. But with minimal concentration, symptoms may not be observed. The dye and iodine usually are excreted after. Increase fluid intake after the procedure usually facilitate excretion of the dye within the next few hours of the procedure. Take care and do keep us posted.
It should usually pass from your urine within 24hrs. Just make sure you increase you water/fluid intake. Effects from the iodine should most likely be immediate, depending on the severity of your reaction. Sometimes there can be irritation, but just plan old soap & water should suffice. If more severe, you can get a topical steroid from your dr.