When you first start a DIY CO2 system everything is full of air. The more tubing you use, the more air you have in the system. Before the tank gets much CO2 the air in the system has to be pushed out by the CO2 first. Clearly if you had 10 feet of 1 inch diameter tubing in the system, it would take a long time for much CO2 to make it to the tank. With the 3/16 inch tubing we use, we never have a huge amount of air in the system to purge, but I think it is a good idea to keep the amount of tubing as short as you can and still have it work ok.
Before someone disagrees, it is true that the CO2 coming from the bottle immediately mixes with the air in the tubing, so a little CO2 plus a lot of air is what first enters the tank water. The ratio of CO2 to air improves with time until it is almost all CO2.