According to Gemini:
For a 6-game suspension, the player is typically allowed to return to the team facility and participate in practices after the team's third regular-season game (meaning, during the week leading up to their team's fourth game).
Here's a simple breakdown of the standard rules for an NFL player serving a suspension (whether for substance violations or other infractions):
Before Suspension - Training Camp & Preseason Can practice and play in preseason games.
First Half of Suspension - Games 1, 2, & 3 Cannot practice or be at the team facility.
Second Half of Suspension - Games 4, 5, & 6 Can practice and attend team meetings.
After Suspension - Week 7 (or later) Eligible to be activated and play in games.