Well, let me try and explain how it is at Delta...
Maintenance is scheduled based on cycles and / or hours, depending on the unit involved. When a Delta aircraft overnights at a 'maintenance station' (Delta or contract mechanincs available; no more than 3 days apart), a 'Layover check' is performed. Fuids, cabin gripes, minor daily maintenance are targeted.
After so many layovers (usually about 30ish depending on type) the aircraft requires a 'Service check', which is a bit more indepth.
After so many service checks, the aircraft is scheduled into the hangar for a Mid-Visit (MV). This is heavy maintenance requiring up to 14 days, again depending on type, and what type problems are found. This is about 3 1/2 to 4 years SMOH.
After another 3 1/2 to 4 years, the aircraft returns to the hangar for a Heavy Maintenance Visit (HMV). This is equivalent to a 'zero time', and can take up to 30 days depending on type. Everything that can be disassembled and is required to be is removed, reworked, and reinstalled.
Breaking up this routine are visits to the hangar for Engineering Orders (EOs) which the line cannot complete due to time / manpower, or paint shop visits, and of course repairs of a non-routine nature which either require engineering input or in-depth troubleshooting, as well as ageing-aircraft Corrosion Visits on the 727, 737-200, and L1011 fleets. There are 4 CVs per HMV cycle, and they are scheduled to be performed concurrent with service checks / MVs.
As you can see, there is a lot of room for overlapping of maintenance. For example, during an HMV, there may be four or five card decks issued to open up the vertical fin, due to the fact that a HMV, MV, CV, and service check are all being done at the same time. We open the same panels (mostly), and have to sign off each card independantly.
The real fun is when we are 10 days into a twenty day HMV, and scheduling 'discovers' that a MV is also due. We either have to open up panels already closed or show the inspector where the work was previously accomplished. I have spent hours literally proving that everything has been accomplished!
I hope this isn't too much information, but in a nutshell, transport category aircraft are ALMOST ALWAYS being inspected, so there isn't a need for a dedicated 100hr,