The simplest approach is to let user input any time they want, and it’s the firmware’s job to quantize the value as necessary. But this may cause some confusion (like they may be surprised that 3 minutes and 10 seconds get rounded to 3 minutes). So the better approach is for the UI to match the firmware: for example, the user can put in any number in the ‘second’ box, but as soon as the ‘minutes’ box has a non-zero number, the ‘second’ box is disabled to reflect the fact that beyond 1 minute the accuracy become minutes.