My idea;
timer.simple - set time and function to run - every minute = good idea.
in function,
check if current time equals ( previously sched time) - Yes, restart. (you'll have to figure out some rounding tricks to account for variance, timer might not run function until .25 before or after your scheduled time.
check if current time is greater than ( previously set time var - 10min ) and less than (previously set future time) Yes? Display ( set time - current time) which will be (10, 9, 8 ...) each time looped.
set specific (static server time?) (manually set time 10 min from now?) variable -
run the timer.simple again
end