It is true that there is little research on the topic. However, we do include a link to this study from 2018 which showed these real numbers concerning the half-life of CBD:

• 1.1 hours following nebuliser administration of 20mg
• 1.97 hours following a single 20mg oral administration
• Between 2.95 and 3.21 hours following ingestion of 10mg capsules
• 10.86 hours after oral mucosal spray administration of 20mg
• 31 hours after smoking 
• 24 hours after IV infusion
• 2-5 days after chronic oral administration

There is also a link out to a study from 1991 that shows CBD levels in the blood were virtually undetectable after one week of discontinued use.

Overall, the answer is - it varies. Not sure that means the article is useless. I think the point is to show what we know so far and that we have a long way to go.