Get last 20 minutes average value of object

[Odd Egil Aasheim]

I updated the script to work with 2 byte float, You have to write value to the object after you start to log it.

I've tried to make this script to calculate average within the current hour, but is unable to make it work.

Have tried to substitute  time= os.time() - pastTime  with  time= os.time() - os.time("%H") and a couple of other formats
but get the following error 
User script:5: bad argument #1 to 'time' (table expected, got string)
stack traceback:
[C]: in function 'time'
User script:5: in main chunk

Also tried to use a GA as a local reference for this where the value at is updated at every new hour.

How can it calculate values from say when time is 22:48, back towards 22:00