Make Bash report the start times all commands, and total durations of long-running ones.

.prompt-time

export _ps1_timer

function _ps1_timer_start {
  # echo START
  _ps1_timer=${_ps1_timer:-`gdate +%s%N 2> /dev/null || date +%s%N`};
}

function _ps1_timer_stop {
  # echo STOP
  if [ -z "$_ps1_timer" ]; then
    return
  fi
  local nanoseconds=$((`gdate +%s%N 2> /dev/null || date +%s%N` - ${_ps1_timer:-0}))
  _ps1_timer=

  local milliseconds=$((nanoseconds / 1000000))
  local seconds=$((milliseconds / 1000))
  local minutes=$((seconds / 60))
  local hours=$((minutes / 60))

  local milli=$((milliseconds % 1000))
  local hecto=$((milli / 10))
  local deci=$((hecto / 10))
  local second=$((seconds % 60))
  local minute=$((minutes % 60))
  local elapsed
  if   [ $milliseconds -lt 200 ]; then elapsed=
  elif [ $seconds -lt 1 ];       then elapsed=$(printf "%d ms"                                         $milliseconds)
  elif [ $seconds -lt 10 ];      then elapsed=$(printf "%d.%02d s"                            $seconds $hecto)
  elif [ $seconds -lt 100 ];     then elapsed=$(printf "%d.%d s"                              $seconds $deci)
  elif [ $hours -lt 1 ];         then elapsed=$(printf "%d min %02d s"               $minutes $second)
  else                                elapsed=$(printf "%d h %02d min %02d s" $hours $minute  $second)
  fi
  if [[ -n "$elapsed" ]]; then
    echo $'\e[90m'"($elapsed)"$'\e[0m'
  fi
}

export _ps1_timer_enabled=

function _pre_command {
  if [ -z "$_at_prompt" ]; then
    return
  fi
  unset _at_prompt

  if [ -n "$_ps1_timer_enabled" ]; then
    local timestamp=`date +'%H:%M:%S'`
    echo $'\e[90m'"$timestamp"$'\e[0m'
    _ps1_timer_start
  fi
}

_first_prompt=1
function _post_command {
  _at_prompt=1
  if [ -n "$_first_prompt" ]; then
    unset _first_prompt
    return
  fi
  _ps1_timer_stop
}

PROMPT_COMMAND="$PROMPT_COMMAND"$'\n''_z --add "$(pwd '$_Z_RESOLVE_SYMLINKS' 2>/dev/null)" 2>/dev/null;'$'\n''_post_command;'

function prompt-time {
  case $1 in
    y|yes|on)
      _ps1_timer_enabled=1
      trap '_pre_command' DEBUG
      ;;
    n|no|off)
      _ps1_timer_enabled=
      trap - DEBUG
      ;;
    *) echo 'usage: prompt-time (y|yes|on|n|no|off)' ;;
  esac
}

help.md

Prints current time whenever you start executing a shell command, and the elapsed time in the end if the execution took more than 0.2 s.

Example:

pyrtsa ~ $ sleep 0.1 && echo 'Done waiting.'
10:43:34
Done waiting.
pyrtsa ~ $ sleep 1 && echo 'Done waiting.'
10:43:37
Done waiting.
(1.06 s)
pyrtsa ~ $

Usage: Add the following to your .bash_profile or .bashrc:

source ~/.prompt-time
prompt-time on

(On macOS, requires gdate, i.e. brew install coreutils.)