an A check is dependant on approved maintennace planning documents (i.e. combine what the OEM states and your NAA requirements) and operator experience.
About only 40% of our A check is what the OEM requested, the rest is based on what we wish to perform from past experience (e.g. lub of flap bearings we find that seize, checking expiry dates on emerg equip, checking whats gone missing/damaged (mainly documentation) and operation check of items not used a lot e.g. megaphones)
So our A check, is baiscally emerg equipment check and lub of flight controls and landing gear, with some general visual inspections of airframe and a few operational tests such as autopilot.
A single aisle twin engine turbofan aircraft and it takes 2 persons 12 hours to perform, but aircraft not taken off schedule or into a hangar. Its done on the line between flights.
We do not do phased maintenance checks, so others may have larger A checks than us as they phase in B cand C check tasks (to use pre-phase check terms)