Space Marine Phase
At the start of the Space Marines' turn, each player rolls one six-sided die to determine the number of command points they will have until the end of the turn. Command points represent tactical suggestions or advice given by the leader of that squad. They can be spent on units from that squad to give them additional action points. They also are the only way to spend action points during the Tyranid Phase. Each model must complete its entire 4 AP before another model in its squad can use its action points. Because of this limitation, command points are also a way to stagger a squad's moves, useful in reorganizing their rank and file.
Additionally, if a Commander is used (a 6+ player game option), the Commander rolls another six-sided die. These "Commander" command points can be given out to any unit, not just the units attached to his squad.
If the leader (sergeant or captain) of a squad is killed, then that squad no longer rolls to receive command points. Similarly, if a Commander is killed, then the additional army-wide command points are no longer rolled. Those points do remain usable for the remainder of the turn in which the leader died.
Command points are not saved. They are reset to zero during the Record Keeping phase.
The digital timer is handled by the one of the Tyranid players to keep track of the length of the Space Marine main phase. The Space Marines have a base of 90 seconds to carry out their main phase. They also receive or lose additional seconds on the timer based on the following factors.
If a rules or LoS dispute arises that eliminates or has the potential to eliminate a significant portion of time, a time-out must be taken until the issue is resolved. No play may occur during this period and the clock is paused.
This is where the action happens. Each Space Marine model has 4 action points (APs) to spend during their timed turn. A player may spend action points in any way they wish. The brunt of these points are spent moving, turning, shooting weapons, and going on overwatch. Once a player begins to use a unit's initial 4 action points, all of those points must be used before another one of those player's units may use their initial 4 action points, or the first unit's APs are wasted. This rule excludes additional command points rolled at the start of the phase.
To accomplish all this moving, turning, and killing, read the Game Mechanics section next.