How do I adjust the time Mac Mail takes to mark messages "read"?

It takes a number of seconds before Mac Mail marks a message as "read". I would like for it to take no more than 0.5 seconds, though instantaneous would be best.

How can I adjust the time required to view a message before it is no longer considered "unread"?

Mac OS X, 10.9.4 and 10.10

Solution 1:

Have you tried quitting Mail, launching a Terminal and putting in

defaults write com.apple.Mail MarkAsReadDelay 0

Solution 2:

When utilizing an IMAP account, you may see a delay in marking read when connected to the mail server, as it issues the mark read command to the server first and waits for a response before doing so locally.