How to turn a timestamp (2017-09-17T19:25:27.9843202Z) into a os.time() value?

That timestamp you posted is in ISO-8601.

After some Googling, I found that someone made their own function to convert this into UST (Unix Standard Time), which is what os.time() returns time as.

-- https://forum.rainmeter.net/viewtopic.php?t=23486
function TimeStamp(dateStringArg)

   local inYear, inMonth, inDay, inHour, inMinute, inSecond, inZone =     
  string.match(dateStringArg, '^(%d%d%d%d)-(%d%d)-(%d%d)T(%d%d):(%d%d):(%d%d)(.-)$')

   local zHours, zMinutes = string.match(inZone, '^(.-):(%d%d)$')

   local returnTime = os.time({year=inYear, month=inMonth, day=inDay, hour=inHour, min=inMinute, sec=inSecond, isdst=false})

   if zHours then
      returnTime = returnTime - ((tonumber(zHours)*3600) + (tonumber(zMinutes)*60))
   end

   return returnTime
end

And you can use it like this:

local t = "2017-09-17T19:25:27.9843202Z"
print(TimeStamp(t)) -- 1505676327, which seems about right.

This is really easy using multiplication.

function ConvertYear(value) --converts a year to seconds
    return value *3.154e+7
end

function ConvertMonth(value) --converts a month into seconds
    return value * 2.628e+6
end

and so on. Also, months may not be accurate as they can have 29 days, 30 days, or 31. Why would you want to convert this to seconds? It is harder to read when it is in seconds.

Hope this helps!