How much time does it take to transform supplies into product (Weed, Cocaine,etc)?

That depends on if you've bought any further upgrades to your business. Please see the table below.

The time will vary from business type, and also if you've upgraded your business.
For weed businesses it takes:
8 hours with no upgrades.
6,67 hours with 1 upgrade.
and 5,3 hours with 2 upgrades.

For Cocaine businesses it takes:
8,3 hours with no upgrades.
6,67 hours with 1 upgrade.
and 5 hours with 2 upgrades.

It's worth noting that some businesses require more or less supplies to make product. For example, it requires a full supply bar to make just one single bar of methamphetamine.

You may also try selling product after some time, again the time varies on the business type. Please examine the table below.

For weed businesses it takes:
6 minutes with no upgrades.
5 minutes with 1 upgrade.
4 minutes with 2 upgrades.

For Cocaine businesses it takes:
50 minutes with no upgrades.
40 minutes with 1 upgrade.
30 minutes with 2 upgrades.

Source: GTA Online Guide - How to Make Money with Bikers DLC .