Misc. Dialplan Tools sleep
From FreeSWITCH Wiki
Pause the channel for a given number of milliseconds, consuming the audio for that period of time.
Calling sleep also will consume any outstanding RTP on the operating system's input queue, which can be very useful in situations where audio becomes backlogged.
To consume DTMFs, use the sleep_eat_digits variable.
<action application="sleep" data="5000"/>