Weapons that fire more than one round in an Action Phase suffer from an escalating recoil modifier as the rounds leave the weapon. Semi-automatic weapons that fire a second shot receive a -1 dice pool modifier for the second shot only.
Burst-fire weapons receive a -2 recoil modifier for the first burst fired in that Action phase and -3 for the second. Long bursts suffer -5 (first burst in phase) or -6 recoil (second). Full auto bursts suffer -9 recoil.
They could have simplified this by saying that recoil is cumulative, SA has no base recoil, Short Burst has -2, Long Burst -5, Full auto -9. The second time you fire a weapon in an action phase, you suffer an additional -1 penalty.
So to answer you question directly, we go look at combat turns.
Combat Turns may be broken up into a series of Initiative Passes if any character have the ability to take extra actions in a Combat Turn. The point during each Combat Turn when a specific Character can act is called an Action Phase.
So each time your initiative comes up during a combat turn, you get an Action Phase. This is further emphasized by the Sequence which follows (SR4A, pg. 144):
1. Roll Initiative
2. Begin First Initiative Pass
3. Begin Action Phase
4. Declare and Resolve Actions of Remaining Characters (repeat step 3 for each successive character, in descending initiative order)
5. Begin Next Initiative Pass (repeat steps 3 and 4 for characters with 2+ Initiative Passes)
Thus, the penalty only lasts for that specific initiative pass.
