Terran Timing Push vs. Zerg
From Liquipedia Starcraft Wiki
In the Terran vs. Zerg match-up there are points at which Terran can punish Zerg with timing attacks. One of these points is the midgame Timing Push in which Terran attempts to break the natural expansion Sunken wall to end the game before it reaches Hive Tech. At this point in the game Zerg has taken their Third Gas Expansion but has not yet reaped the rewards of running three Extractors and thus cannot afford Hive Tech units. The Timing Push aims to exploit this temporary weakness.
 General Timing
The timing window for this build begins when the Queens Nest pops and ends when Zerg reaches Defiler tech. Terran at this point has reached Science Vessel tech, has 1/0 or 1/1 infantry upgrades and is able to assert themselves against Mutalisk harass or Lurkers out on the field. Terran must also be able to pump units from six production facilities uninterrupted.
 Build Order
In general, you begin with either a 1Rax FE or 2Rax FE and start your factory tech between 40-50 food, constantly teching until your science vessel pops out. If you wish to go SK Terran, you can discontinue factory production after a few tanks (or skip it altogether) and add another starport instead.
While it is difficult to give supply counts for builds in middle and late game, there are some rules of thumb that help align the Timing Push:
- Terran should have beaten back Mutalisk harass or broken Lurker contain. This prompts Zerg to take the third gas.
- Terran should be able to pump units from the following buildings:
- Three to four Barracks pumping Marines and Medics
- One or two Factories building Siege Tanks
- One or two Starports building Science Vessels
- For a total of six production buildings
 Pushing Out
The Terran army should be able to push out to the Natural expansion and set up at the natural choke. Initially it is good to set up within siege range but not move in with Marines and Medics until Zerg attempts a counter. This way Terran can protect against a flank while still breaking down the Sunken Colony wall. Once the Sunkens are down Terran can push in with Marines and Medics and attempt to drop the Hatchery. A few things to remember:
- As it is a push, it is important to move your forces slowly as to not get flanked by Zerg's quicker speed.
- Don't try and force your way through until after the Sunkens are down unless you have to.
- Letting your Science Vessels get Scourged is a surefire way to get your push wiped out by Lurkers.
Even if you are unable to break the natural and end the game then and there are Timing push provides a good screen to match Zerg's Third Gas Expansion and keep them from getting an economic advantage. After that it's time to hunker down and prepare for late game play.