America Online Inc has responded to complaints that it has given users insufficient notification that it was moving those that did not ask to stay on the $9.95 for five hours and $2.95 an hour thereafter rate over its new flat $19.95 a month unlimited access rate by agreeing to give users more time and information to state their preference. Customers automatically switched to the new plan on December 1 will be able to change back to the original plan any time up to April 10 with a refund of the difference.