There's no need to stare at the screen and wait for the bar to decrease :-) After a little bit of fishing you can settle into an easy routine of reading your favourite book while listening for the audio que when your bobber splashes. My routine is very simple:
- Cast bobber
- Position mouse pointer over cursor
- Read book :-)
- Right click on splash sound (optionally shift-rightclick for autoloot)
- Cast again
If you never get the splash then recast once the bar runs out. You'll soon develop a feeling for how often to recast.
There's two kinds of fishing for me. First is casual (waiting for a group to form or waiting for a boat) where I fish until I whatever I was waiting for happens. Second is goal-oriented where I fish until I pull up a non-fish item (for example a chest) or a full stack of Firefin/Blackmouth. That way the fishing experience always ends on a high note with a sense of achievement. It's also a real nice way of winding down after a session, just go fishing for a bit while chatting with guildies or your group and talking about what went well, how to divvy loot etc.
Oh and avoid fishing in areas where you get a lot of 'your fish got away' messages. That justs builds up frustration.