I see where you're going Vvwmarle, but let me correct a misapprehension first.
The timer would be in the care of a single official during any day's gaming, and he alone would be in charge of all of the kit - at no time would any player be required to handle the cards, nor the timer, so the question becomes one of whether the official benefits from the ability to rapidly alter the parameters of the timer between one state of play and the next and not one of security.
To this end I've probably settled on the idea that I'll approach the design as a hybrid, which will allow the user to dig in to a menu if he/she desires/needs, but where the rfid card, containing all the parameters for a particular setup, would obviate the need to do so.
This would also permit me to update the timing systems already deployed without having to get my hands on them. Bonus.
One question I still have: What is the likelihood of cards getting corrupted? I cannot find much in the way of information on this topic that doesn't talk about hammers and microwaves. I'm of the impression that the cards, once written, remain reasonable stable unless intentionally harmed.
wvmarle:
Part of the appeal of RFID is that it's so cheap that tags can be disposable (especially the very simple ones that are basically an electronic bar code), ...
...you can gain lots of efficiency: store start and stop time in a single byte, for example).
That byte-level access appeals. And, lastchancename, arrays of structs - yes.
Ho hum - lots more to learn for this old dog 