Not for sentencing timelines, but virtually nobody (less than 0.5% of all drug offenders) doing federal prison for drugs is in there for mere possession. [0]
The feds aren't going to get you for possession. That's more of a state level thing. If the feds are getting you for drugs it's because you had massive amounts, or crossed state lines with them. Ironically and sort of counter to your citation, simply possessing drugs while crossing state borders is considered trafficking.
[0]: https://bjs.ojp.gov/content/pub/pdf/dofp12_sum.pdf