Add maxlength of 6 for time correction in preferences

Add maxlength of 6 for time correction in preferences

* Supported formats (controlled by filterTimezoneInput) are:
** -12:34/01:23.  It says, "Max is +14:00 and min is -12:00", both
   of which fit in 6 (if someone uses -24:00/+24:00, it's the same width
   anyway).
** If it's not in that format, it's treated as a simple hour, which
   means it should be from -12 to +14 (max 3).

Bug: 70405
Change-Id: I47ec2c07929069cb5243c306a1c502751e57a31b