Yes a visitor needs to opt-in to start the mining process and earn JSE tokens. The longer they are on the site for the more tokens the publisher can potentially earn. No cookie but there are restrictions on the IP address of visitors to prevent abuse.
I know we have the stats page on the explorer https://blockchain.jsecoin.com/#/Stats
that tells us how many unique hits per day we have in total. But what are the daily earnings? Can we calculate an average earnings per unique hit for publishers?