Your question is not clear. Are you referring to the time allocated for the welder to weld the test coupon or the time between the initial qualification and subsequent requalification?
In the first case; welding standards do not place a time limit on the time needed to weld the test coupon. Some companies may impose a time limitation, but that isn't a code requirement.
In the second case; most AWS welding standards allow the welder's qualification and certification to be "extended" indefinitely if the employer can show continuity.
There are also limitations on expiration when process use doesn't take place, and also rules in the various codes specific to elapsed time between a failed test and a retest. We need some more information to answer accordingly.
