Do we just have to link our Twitch to speedrun.com or have a timer visible on screen or use certain keywords?

I think you need to be affiliate (or is it partner?) and have your stream linked in your profile

From this thread: https://www.speedrun.com/streaming_recording_equipment/thread/41ght it appears you just have to link your Twitch account into your SR.C account (which you have done), select a game for the stream, and it will show on the streams page automatically.

Two more requirements for that to work, though - the game itself has to be in the Twitch games database, and the leaderboard on this site has to be linked to the game name on Twitch (which is done by the game moderators).