This option lets you control for how long will Nping wait before
sending the next probe. Like in many other ping tools, the default
delay is one second.
<time> must be a positive
integer or floating point number. By default it is specified in
seconds, however you can give an explicit unit by appending
ms for milliseconds, s for seconds,
m for minutes, or h for hours
(e.g. 2.5s, 45m, 2h).
--rate <rate> (Send probes at a given rate)
This option specifies the number of probes that Nping should send
per second. This option and --delay are inverses;
--rate 20 is the same as
--delay 0.05. If both options are used, only the
last one in the parameter list counts.