Just spoke to an extension office about grafting my apple trees into containers. He told me to get my rootstock now and plant them into the containers to start to establishing the root systems and graft the scion in late winter or spring. He told me that he thinks it would be a very low success rate if I get the rootstock and graft the scion on and then plant it into the containers. Remind you it is Mid October here. That goes against everything I have read. Your thoughts on what he has told me would be appreciated.

You can move the rootstock when the trees are dormant and the ground is not frozen. If you have the time, and can protect the trees (from extreme cold/nibblers) during the winter, then planting now makes sense as it will be one less thing to worry about in the Spring. I find that the professional nurseries do a much better job of protecting the trees than I do, so my preference is to have the rootstock delivered in late winter and graft a few weeks later in early spring.

A friend of mine would hold/refrigerate apple bud wood till June and graft the rootstock in June.  This way the root stock is active and can support the bud-wood as it comes out of dormancy.  You might as well try a few different things and see what work for you.