I can confirm that the hard cap is 35s whatever you do. I didn't know this before and spent some effort getting the synergy item with -5s on it, only to find that the timer itself would "sometimes" show 30s but an extra 5s would have to pass before you could actually make the shot.

There seems to be a bug in the code for whenever you surpass the hard cap of 35s, which is most likely related to the 2 QD stacking mechanism. You'll see the wrong time shown for the next shot.

When they first added the 2 QD stacking mechanism, people were able to trick the timers into showing -2s or similar using the right gear and were able to QD over and over with no delay (you'd see CORs soloing ZNMs with QD kiting). They fixed that but there is still an issue showing the right recast timers when using more than -25s QD gear/JP/MP.