I have run into this same problem with the product in the past, and almost every time I have, it's been because of high humidity in the garage. Two things have helped:
Sanding with a 320-400 grit paper between the coats. This helps knock down the bumps.
Using a fan during the drying process. I use a heavy duty fan, and it seems to speed up the drying time. Once it's aired out a little, I put it in the basement and it's completely dry within a day.
*Something else you could consider is putting one coat of oil-based polyurethane or varnish over the top of it. Wood Magazine recommends trying this in their article reviewing the product.
Here is the review I found: Minwax Antique Oil Finish Review