Being active in the reserve components (Air Guard/ AF Reserve) simply means being the time being there doing something that is military duty connected to generating getting pay and eligibility for other entitlements and benefits. Being in active duty status while going through Basic Military Training (BMT) and subsequent training for award of 3-level AFSC (graduating the AFSC's apprentice course) does not necessitate being in the Active Guard Reserve (ARG) Program.
The ARG Program exists for personnel who are responsible for assisting in the organization, administration, recruitment, instruction or training of ANG personnel and assigned primarily against mobility positions. However assigned primarily against mobility positions doesn't by itself require being in the ARG Program.
The active duty commitment however is significant when Air Guard and AF Reserve students are attending a training course for 20 weeks or longer. Presumably Air Guard and AF Reserve students are PCSed to the Apprentice course (pararecue-Kirtland AFB) and combat control-Hurlburt as the Regular Air Force (Active duty) students are. It is reasonable for the reserve component student to expect being on continuous uninterrupted active duty in training status for at least two years.
The situation and circumstance of getting entry classified into Pararescue, Combat Control, and Special Operations Weather through a reserve component enlistment varies between these AFSCs and the units as much depends on the position being filled and the unit's mobility and response to emergency domestic situations demands. For example the 212th Rescue Squadron responds to emergency domestic situations with in the state on a daily basis and frequently deploys to natural disasters occurring in other states. The demand for having personnel in the ARG program is typically greater for this unit than for units in other states.
―Immediate Response‖ is defined by DoDD 3025.15, paragraph 4.7.1. as ―any form of immediate action taken by a DoD Component or military commander to save lives, prevent human suffering, or mitigate great property damage under imminently serious conditions when time does not permit approval from higher headquarters.
Pararescue is a National SAR resource, so this would be more applicable to pararescue more so than combat control, special operations weather, or TACP.
The only useful solid answer to the question is to ask it of each reserve component Rescue and STS unit as the answer may and can differ among the units.