Maybe I'm missing something, but the linode FAQ says:
How am I billed?
We currently offer monthly, annual, and 24-month billing cycles. If you are interested in pre-paying, open a support ticket and we can accommodate you. When you sign up, your first invoice is pro-rated until the end of the month. After that, your subscription is automatically renewed on the first of each month (for annual accounts, on the anniversary of your first full month).
Taking another look at the linode site I can definitely see where the confusion might come in as it's difficult to find any indication that costs are calculated daily. However I did find the following, again from the FAQ:
Can I upgrade my Linode?
[...]
Removing resources pro-rates the balance of the month back to your account so you only pay for the time you've used them.
Edit: I've just gone into my linode account and the removal link does give you a figure for how much you'll get back. You pay for a month in advance but if you don't need the full month you can remove the linode and get your money back for the time remaining.
How am I billed?
We currently offer monthly, annual, and 24-month billing cycles. If you are interested in pre-paying, open a support ticket and we can accommodate you. When you sign up, your first invoice is pro-rated until the end of the month. After that, your subscription is automatically renewed on the first of each month (for annual accounts, on the anniversary of your first full month).