Duty-cycling is commonly used to reduce power consumption at non-peak data rates. Adaptive wireless networks may require very small duty-cycling ratios at very low data rates, or very short cycle durations for minimum latency. This paper studies the required turn-on and turn-off times as well as the idle power consumption for efficient operation even in the most extreme duty-cycling configurations. To research realistic values thereof for medium output power levels, a 19 dBm 400 MHz inverse Class-E power amplifier (PA) is designed. A two stacked Heterojunction Bipolar Transistor (HBT) switch is employed to increase the possible supply voltage and a CMOS inverter based input stage is used to allow drive from a digital output. The PA has an efficiency of 44 % operating from 3.5 V. Turn-on and turn-off times are below 20 ns and idle power consumption is 166 nW allowing efficient aggressive duty-cycling operation.