The existing commercial controllers from decades ago use extremely simple programs, they don’t account for dynamic events, the programs don’t overlap with each other, most of them also don’t pull weather data online to determine the dynamic water time. For those kind of simple programs, it’s certainly possible to do a simple look up to figure out what program should be running at any given time.
If you have long watering sessions, you can break them into smaller intervals using the ‘repeat every’ feature available in the programs. For example, instead of watering for a continuously long 12 hour session, set it to water 15 minutes at a time and repeat 48 times. This way, if the controller reboots in between, it at most loses a 15 minute session but the next repeat cycle it will run again. The user manual specifically mentions this ‘repeat’ feature as a way to break down long water sessions into smaller blocks.
Above all, the entire project is open-source. If you feel one feature is missing and needs to be improved, why not modify the code to implement it yourself? You can do it in anyway you want, and don’t have to wait for us to implement it for you.