What is the grammatical rule of the usage in the format of "a full six months"?
Here is a real world example of this grammatical format from Forbes:
Once newcomers feel comfortable with market concepts, Sebastian also favors “paper trading” before putting down real money. At the start of his career, he paper traded for a full six months.

Source Link:
https://www.forbes.com/sites/kitconews/2012/02/17/mark-sebastian-emphasizes-importance-of-understanding-math-behind-options/2/#39e5a88d5f23

How should this "a full + a time span" format be used? Can I say something like "a full two years"?

Question

What is the grammatical rule of  the usage in the format of "a full six months"?
Here is a real world example of this grammatical format from Forbes:
Once newcomers feel comfortable with market concepts, Sebastian also favors “paper trading” before putting down real money. At the start of his career, he paper traded for a full six months.

Source Link:
https://www.forbes.com/sites/kitconews/2012/02/17/mark-sebastian-emphasizes-importance-of-understanding-math-behind-options/2/#39e5a88d5f23

How should  this "a full + a time span"  format be used? Can I say something like "a full two years"?

Answer

The purpose is to show that the time frame is completed in its entirety and has not been rounded up. There is nothing wrong with using this with any time span. For example, someone else could have worked on a project from January of 2015 to November of 2016 and not have worked a "full 2 years," even though the average person would round this up to 2 years' worth of work. Unlike someone who worked from December of 2014 to January of 2017, meeting the minimum requirement of having worked a "full 2 years."

Answer

Yes, we can. It's also useful for amounts of money, like "he received the full 10 million dollars." I suppose we can explain it as having an implied singular measure word: "time period of," "amount of," or "sum of."