I think they should be added however definitely no averages of 5 I would go with mean of 3.
The problem would be having an easy way to weed out people who take way over 10 minutes. I think it would be hard to do it without being accused of being unfair.
The best I can think of is hold an opening round where you have to solve the 7x7 under ten minutes,(unless you have a major pop), but do it in a group, for example 15 people show up at a competition wanting to compete with the v-cube 7. All of their cubes are scrambled at they are all solve at the same time with 15 seconds inspection. At the end the judge would call out 10 minutes and they would have to put their cubes down. Those finished would move on to do mean's of 3.
However there could be scenarios in which all of them get done in under 10 minutes, then there would have to be some sort of backup system.
Please offer your thoughts. Do you think 10 minutes is a good benchmark, or should it be raised or lowered? I'm no expert, so please offer your opinions.