Actually, I think 5 games is the length of the suspension for third & subsequent marijuana violations, provided the player agrees to treatment and counseling.
http://members.cox.net/lmcoon/salarycap.htm#51
The CBA does not specify the length of suspensions except in the cases of:
Missing the rookie transition program: 5 games
Unlawful violence: 10 games minimum
Drugs other than marijuana and steroids:
First violation: no suspension
Second violation: 6 month suspension following mandatory treatment program
Third violations disqualfication from the NBA
Marijuana:
First two violations: no suspension
Third & subsequent violations: 5 games
Steroids:
First violation: 5 games
Second violation: 10 games
Third & subsequent violations: 25 games
The suspensions for drugs become larger if the player refuses to submit to mandatory treatment and monitoring.