Are you asking to randomly generate a floor, or continuously generate the pattern of floor your on?
You could set this up using a WHILE statement instead of a timer which will keep generating until a delimiter is used. WHILE player is within a range(not sure if this is set or not), add more floor scenes. If not, remove/null the free_queue.
Have you tested how much strain/threads it would take? If your going for lower-end models it's important to make sure a reasonable/good amount.