As far as I know you can't change the clock's display (not without making a mod or something).
You can display a regular (non-game specific) timer if you want to, but I forget the cvar for that.
Tech's "repair" and "heal" stuff just like they "hack."
Go up to the object or player in question and hold down "use" (they will probably need to be standing still). You'll hear a sound as you're healing/fixing.
Note that only certain objects can be repaired. For example on Siege Korriban you can't fix the beam projectors or gates (sorry). On the other maps you can't repair Heavy Blaster Cannons or Automated Turrets once they are completely destroyed (only when they are damage).
You also can't repair the "walls" on Siege Desert either.
If you see a health bar on something you can repair/heal it usually, with the above exceptions.
All techs can "heal" teammates by "using" them (same as you would repair) except for the Light Jedi Tech (Jedi Healer) on Korriban. She uses Team Heal instead which works just like it does in other team games.
When a Tech "heals" by using, they also gradually give the person ammo, so just hold the key down longer and you'll slowly build up their ammo supply. Simply hitting "use" when nobody is touching you will cause an Ammo Dispenser "Ammo Battery" to fly out of you (there's a status bar showing how long it takes for the next one to appear) and if that is picked up (by friend or foe) it gives a certain ammount of ammo.
All this (and more!) is covered on my site btw, so I suggest you check it out!