As early data on iPad apps trickle in, one thing is clear: It’s going to require mountains of metrics for advertisers to pony up for the new platform’s ads — and their high prices. But early data from Conde Nast will bolster the argument the iPad is worth a premium, as it’s delivering on reader attention better than other media channels. The publisher reports users are spending more than two hours on average with its Vanity Fair and GQ apps — that’s double the average hour spent with print magazines. Time spent with iPad apps also beat digital channels: Two hours with an iPad app trumps an average of 15 minutes on websites and 75 minutes on mobile apps per month.