The boards aren't back from OSHPark yet, but I decided to take an old AC Timer board board and just use it to hold an ATTiny to test out the firmware.
I'm happy to report that that done the firmware works perfectly. It does take up almost all of the available flash space of an ATTiny9, but that's more or less because you have to trade flash for RAM by having every function be always-inline and save the stack for the ISR call and return. Most of the space, however, is taken up by the PRNG. It's the same one used for the Crazy Clock and uses 32 bit operations, which necessitates adding the 32 bit math. Using 16 bit values would probably reduce the size by 25%, but at least at the moment there's no driving need.
I haven't verified the low current draw just yet, but I anticipate that won't result in any surprises.