Install software:

opkg update
opkg install coreutils-sleep
/usr/bin/sleep --help
Usage: /usr/bin/sleep NUMBER[SUFFIX]...
  or:  /usr/bin/sleep OPTION
Pause for NUMBER seconds.  SUFFIX may be 's' for seconds (the default),
'm' for minutes, 'h' for hours or 'd' for days.  Unlike most implementations
that require NUMBER be an integer, here NUMBER may be an arbitrary floating
point number.  Given two or more arguments, pause for the amount of time
specified by the sum of their values.

Usage:

/usr/bin/sleep  0.001