When Pandora is streaming music on a website, the player will automatically stop playing after one hour if you haven't interacted with it. This is to conserve music royalty fees and bandwidth costs in the event someone is no longer listening. You can keep Pandora from logging out by remaining active on the website while music is playing.
Log in to your Pandora account and start one of your stations.
Interact with the Pandora website within an hour of starting the station. Click the thumbs up or thumbs down buttons on songs, skip songs, switch to a different station or search for a new artist or song. Most actions on the Pandora website, from telling Pandora what you think of a song to clicking on links on the page, count as an interaction and keep Pandora from timing out.
Upgrade to a premium Pandora account, called Pandora One, to increase the timeout period to periods longer than one hour. Pandora One is also ad-free.