I feel that for Tactics Trainer, there should be an option to turn off the timer.

I feel that way because sometimes TT gives me an easy problem and gives me 26 seconds (or so) to do it. In a real game, I would not have spotted the tactic, but seeing the 26 seconds makes me look for obvious material gain, checkmates, etc.

Or maybe, you could have an option where the clock counts up instead of down, so you can think as long as you want, and there's a specific pass time (say, 1 minute) or something?

I dunno.

you can turn off the timer and still play it rated, so it doesn't distract you...I know what you mean, you see 300 secs and you relax and have a good look, you see 26 secs you have a tendency to jump in quick and guess.  I've learned to try and figure it out and not guess and my rating has improved.

Go to settings on your tactics trainer page and you will see the option to not display the timer, you can also play not rated and just try to solve the problems, you can then select a range of difficulty to play at.

I did that for a while and improved a lot and then went back to rated.

On the Tactics Trainer setting page at http://www.chess.com/tactics/settings.html you can change the "Training Mode" to "Unrated" and also turn off the timer so that it does not show. Once you have updated the settings to your liking you can click on the "Save Preferences" button at the bottom of the page.

I can't change my setting - why?

It's grey and you can't click, while other settings are black and you can click.

IM A DORK!!!!!!!!! lol