First of all, thank you very much for taking the time to write and for your kind words, I really do appreciate them! :^)
It is difficult to say how long the migration process should have taken, as this heavily depends on the speed of the hard drive of your older Mac, as well as its level of fragmentation. Indeed, some older models (especially laptops) used to ship with drives that, while advanced for their time, feel awfully slow nowadays which is reinforced by the fact that we are used to see transfers with our iPods and external drives go at blazing speeds.
Should the resulting installation be stable and in good shape, chances are nothing went wrong and the delay was just due to hardware considerations.
Let me know if this helps!