As far as I can tell, there is no such limit. The official Rules for the FIS Alpine Ski World Cup define only:
3.6 Limitation for SL / GS / DH in 2 runs
Limitation for the 2nd run (Slalom / Giant Slalom / DH): Only the first 30 competitors from the 1st run are qualified. This limitation is not valid for the Alpine Combined (see art. 9.5.1).
(And as noted, the Alpine Combined does not have even that limit:
9.5.1 Alpine Combined
All competitors who complete the 1st run correctly have the right to start in the 2nd run.
I did not find any more stringent criteria. The more general International Ski Competition Rules define the following for slalom races (and similarly for the other race types):
806.2 Limitations in the Second Run
The Jury has the right to reduce the number of competitors for the second run to half on the first run start list. The decision has to be made no later than one hour before the start of the first run.
But again, no specific time limit.
However, note that competitors who have more than 108% of the total time of the winner will receive no World Cup points:
10.2 Time difference from the winning time
If a competitor's overall time (at combined events the total running times of both events counting for the Combined) is more than eight (8) percent greater than the winning time, irrespective of the rank achieved, no points will be awarded