Grow light time control script

[clue9]

Hi.
My soulmate is working with plants these days, and wants ligths to turn on and off in specified times of day.
I try to make a script to make here able to automate and decide this from Moasic.
Created 2 virtual groupadresses for on and off time (hh:mm), and made a time widget in Moasic for her to change times at her own will..
Group adresses is formatted as 3byte time/date.

Then I wrote this resident script to run every 60 seconds.
But it fails in many ways. I tried to log output but get errors.
Someone want to help out?
Could it be different time formats? first log entry returns a nil value, so why is it not reading my object data?

Code:

on_time = grp.getvalue('31/1/13')
off_time = grp.getvalue('31/1/14')
--log entry to confirm data is read
log(on_time)
log(on_time)

--log state of light to confirm change
    lightstate = grp.getvalue('31/1/17')
    log('Light turned off at ' .. os.date('%H:%M:%S') .. ' set to' ..ligthstate)

-- time set as hour and minute. Seconds never used when set, will always be 00, datatype is 3 byte time/day this is tested ok.
--as time is set by only hour and minute and seconds is never set in the on and off times, seconds have to be equal 00 when comparing. (3 byte time/day)
if os.date('%H:%M:00') == on_time then
    grp.write('31/1/15', true)
  --log state of light to confirm change
      lightstate = grp.getvalue('31/1/17')
    log("Light turned on at " .. os.date('%H:%M:%S') .. 'set to' ..lightstate)
elseif os.date('%H:%M:00') == off_time then
    grp.write('31/1/15', false)
  --log state of light to confirm change
    lightstate = grp.getvalue('31/1/17')
    log('Light turned off at ' .. os.date('%H:%M:%S') .. ' set to' ..ligthstate)
end