i agree.
The value of your service to a user isn't going to increase simply due to the passage of time or growth of your site.
i disagree. many users may not pay on the first day because they don't see the value in it, or don't understand how the site works. but being able to use it for free and coming to depend on it may put a higher value on it over time.
how many users would pay $1 per month to access facebook now that all of their friends are on it and they use it every day? probably a lot. those users probably wouldn't have signed up for an account in the first place if they had to enter a credit card number.