Is it ok to wait several days (after undercoating) before applying an oil-based top coat?
Yes, it's okay to wait 5-6 days before applying the top coat.  The only consideration would be the settling of airborne particles on the surface during the intervening time period (ie. such that may occur because of nearby construction or cooking within the home and/or the use of fans which may stir up a significant amount of dust).

Note, per the spec sheets of the products you are using, there is a minimum amount of drying time between coats; not a maximum amount of time.