Breaks in my honda civic are screeching, and it's even worse when I back up.?
 

How Long Can I Wait Till I Have To Take It For Repairs?

you should take it now

You're hearing the wear indicators, they screech like that on purpose, to let you know you need to replace the pads. You may need to replace the rotors as well, and don't forget to have the rear brakes inspected.You can wait until you hear bare metal rubbing against bare metal and you can't stop, but that would be stupid. Replace them NOW and it will be MUCH cheaper than replacing them later.

You should have taken it in at the first indication there was a problem. The longer you wait, the more damage is done and the bigger risk you run of having an accident by not being able to stop.