I just tried your adverting-supported version, and found it very useful for the sport of Eventing. I am hoping that you might consider a few additional features, which would make a very large positive difference (at least for someone using it for sport purposes):
– Enable users to specify a countdown time to seconds (i.e., hours, minutes, and seconds), instead of just hours and minutes. This would make the app more useful, when the user is trying to beat a time that is specified to the second.
– Have the digital display of the countdown time automatically adjust the number of digits to match the order of magnitude of the countdown time. In other words, if the full countdown time is only in minutes and seconds, there would be no “00:” in the hours position. This would help make the display less crowded and therefore more easy to read at a glance.
– Have a “count up” option, to continue measuring time after the countdown has elapsed, until the user presses “Pause” (or Stop). This would allow users who did not meet their target times to know by how many seconds they exceeded their targets.
– Have an option for the disc to change colour at a specified time within the countdown time, which would serve as a visual second warning (in addition to the sonic “early warning”). Ideally, the user would be able to choose if the two warnings happen at the same moment or at different moments within the specified time.
– Make the “Pause” / “Resume” button the entire screen (other than the area occupied by the “Reset” button), so that users can more easily tap to start or end the timer if they are in motion and their hands are unsteady.
– Allow users to specify the disc and text colours using hex/RGB/CMYK numbers. This is a very minor matter, but it would be useful to users with team colours.
– Have an option for the disc to have a three-dimensional, gradient colouring. This is purely a cosmetic suggestion.
I am not a programmer myself, so I have no sense of whether these suggestions would be simple or horrendously complex to implement.