I'm reasonably certain this is false? I've started Fuck actions with substantially under 1000 flux and finished them before the end of the loop with high enough stats, and completed 30 repeats of a 300-flux action within 4500 flux. I've also timed how long each copy of a ×20 action takes, and with high multipliers they get notably faster (my current first action of a Lift Weights ×20 takes about 3/2 the time the last Lift Weights in that set needs, counting by number of animation shifts per action completion). Speed Up might also be doing something but stat levels dramatically accelerate actions.
(Also, from running a single-action loop which freezes rather than looping at the end I am quite sure a single Chat Up gains net +101 flux, not +100. Further Chat Ups net more than that in a way which I assume scales with stats.)