Attack-time delay
In telecommunications, attack-time delay is the time needed for a receiver or transmitter to respond to an incoming signal.
For a receiver, the attack-time delay is defined as the time interval from the instant a step radio-frequency (RF) signal, at a level equal to the receiver's threshold of sensitivity, is applied to the receiver input, to the instant when the receiver's output amplitude reaches 90% of its steady-state value. If a squelch circuit is operating, the receiver attack-time delay includes the time for the receiver to break squelch.
For a transmitter, the attack-time delay is defined as the interval from the instant the transmitter is keyed-on to the instant the transmitted RF signal amplitude has increased to a specified level, usually 90% of its key-on steady-state value. The transmitter attack-time delay excludes the time required for automatic antenna tuning.
References
This article incorporates public domain material from the General Services Administration document: "Federal Standard 1037C". (in support of MIL-STD-188)