What's the difference between hover power and maximum continuous power?

As the name implies, hover power is the amount of power required to hover. If you add people/cargo to the aircraft the hover power increases. Secondarily, it depends on air density as the rotor is more efficient in denser air - less power is required to lift the same weight.

Maximum continuous power (MCP) is the maximum power the engine/drive system should be exposed to for long periods of time. This power level may be exceeded for shorter time periods. For example, there may be 30 second or 2 minute power limits that are substantially higher than MCP (120%+).

I am not sure about takeoff clearances, but as you may already know power decreases substantially in forward flight and hence a helicopter that needs 1.1*MCP to lift off could still cruise around well below MCP. Also, fuel burned in flight reduces weight and power so that less power is typically needed in the final hover/landing. This can be upwards of a 10% reduction in weight.