I took them out of the oven once a couple had melted nearly to (or over) the bottom of the canvas. Using the oven resulted in straight lines to the bottom of the canvas which wasn't exactly what I was wanting. Now that they were soft and melty I used the blow dryer.
We quickly found that using the blow dryer over the top of the crayons made them melt faster then using it in front of the crayons. It also made a bigger mess this way, but I'm impatient and wasn't worried about a little mess at the top of the crayons. If you are worried about wax dripping over the wrapper it is best to use the blow dryer in front of the crayons. Depending on the way you direct the blow dryer you can also affect which way the melted wax flows.
Since these were technically the girls projects they told me where to point the blow dryer and how long to leave it there. Once they decided they were finished we let them dry a bit while we found stuff to hang them on the wall. Since I used stretched canvas I could just hang them immediately with no frame. Here's the final result!