RC calculation

T=RC, so:

          Time

  Resistance   Capacitance

or

      mS	  

  Kohms   uF

or

    Seconds

  ohms      F

The result gives you 1T. This is 1 time period. So for 1000uF and a 1K resistor T = 1000mS

For charging and discharging a capacitor:

1T 63%
2T 86.5%
3T 95% (this tends to be the default usage with 95% considered basically there)
4T 98% (this tends to be considered as 100% charged / discharged)
(in theory 100% is infinite)

Different voltages don't change the time to reach 1T, but will of course change the voltage measured at 1T (63% of the applied voltage).  E.g. if a 12V supply is connected via 1K to a 1000uF cap it would take 1000mS to reach 7.56V, 3000mS to reach 11.4V. Its exactly the same for discharging a capacitor.