The Factory unlock code comes from the database of the manufacturer. The IMEI go to the server of the manufacturer brand, and the code gets generated.
The code generated on the server can only be used against that IMEI only. If anybody uses that code on another device, then that device may be permanently locked. Further, you will lose one attempt also.
So, do not confuse in Factory unlock code and unlock code. There is not much difference in that. Further, if you got any query you can ask from us via our contact form.
Time taken by Factory unlock code to generate for different brands is different. That depends on the brand to brand.
The price is also different for all brands. Check your brand carefully before placing an order. The price is same for same brand for different models.