Here the negotiations did not know the specific time of delivery, so here's one to two weeks, is the use of fuzzy numerals, and give the other to ensure that the negotiations proceed smoothly.
Here the negotiation sit until the specific delivery time is not known, so one to two weeks here, is to use a few words of ambiguity, to the other side to ensure that the negotiations go smoothly.
We don't know the specific delivery time in the negotiation here, so one or two weeks here is to use the fuzziness of numerals to guarantee the other party and make the negotiation go on smoothly.