[Fizzlemizz]

The time between the events is 90 minutes for the login test but once you've started the clock it's then reduced by 15 minutes (the time the event takes) which I didn't account for.

The ticker code would be:

local ticker = C_Timer.NewTicker(1, function() 
    if timeToRun > 0 then
        timeToRun = timeToRun - 1
        printTime(timeToRun, inEvent)
        return
    end
    if inEvent then -- The event just finished
        inEvent = false
        timeToRun = waitTime - eventTime -- Reset ticker timer to 90 minutes wait time minus 15 mins event time
    else  -- Waiting for the next event just expired
        inEvent = true
        timeToRun = eventTime -- And the event is running
    end
    printTime(timeToRun, inEvent)
end)
printTime(timeToRun, inEvent)

Also fixed in my previous post.