Once your payment has been received, your Premium Account will be activated immediatedly.
If you have an active premium subscription, you will see a Pro label after your name on the top right of the screen.
Please goto My Tools - Setting page, and click on the "Pro Account" tab, you will see expire date of your subscription.
Sorry, we do not offer a free trial, but we provide monthly subscription option, so you may cancel at any time with a minimum of 1 month billing.
When your Premium account expires, you will only lose access to the Premium functions. But your saved items don't expires, you can still access them.