Voilà:
on first join:
set {seconds.%uuid of player%} to 0
set {mins.%uuid of player%} to 0
set {hours.%uuid of player%} to 0
set {days.%uuid of player%} to 0
while player is online:
wait 1 second
add 1 to {seconds.%uuid of player%}
if {seconds.%uuid of player%} = 60:
set {seconds.%uuid of player%} to 0
add 1 to {mins.%uuid of player%}
if {mins.%uuid of player%} = 60:
set {mins.%uuid of player%} to 0
add 1 to {hours.%uuid of player%}
if {hours.%uuid of player%} = 24:
set {hours.%uuid of player%} to 0
add 1 to {days.%uuid of player%}
join:
while player is online:
wait 1 second
add 1 to {seconds.%uuid of player%}
if {seconds.%uuid of player%} = 60:
set {seconds.%uuid of player%} to 0
add 1 to {mins.%uuid of player%}
if {mins.%uuid of player%} = 60:
set {mins.%uuid of player%} to 0
add 1 to {hours.%uuid of player%}
if {hours.%uuid of player%} = 24:
set {hours.%uuid of player%} to 0
add 1 to {days.%uuid of player%}
command /knowtime:
trigger:
send "%{days.%uuid of player%}% :: %{hours.%uuid of player%}% :: %{mins.%uuid of player%}% :: %{seconds.%uuid of player%}%"