When is Minimum Safe Altitude Warning triggered? I know that Minimum safe altitude warning (MSAW) alerts ATC and pilots if an airplane is under the risk of controlled flight into terrain.

But when is this alarm triggered? What is the minimum altitude for it to trigger? If a plane is landing, should it be triggered just before landing?

It will confuse ATC if every plane that is landing triggers that alarm.

There must be some limitations. So, what are they?
The system projects the altitude that an aircraft will be at based on recent track and a calibrated "look ahead time" and an expected controller response time.  That value is then compared to a calibrated altitude floor.  If the aircraft is projected to be below the floor, then the controller will be alerted.

The specific values for all those things are calculated to minimize false alarms, accommodate the type of operation and local operational needs.  The values are specific to that facility and that area and so a straight answer isn't exactly possible.

Here are a few interesting resources in case they help.
Minimum Safe Altitude Warning
EUROCONTROL MSAW Guide