Very neat application! Answering your questions, the first option is not currently possible using master station option. However, it is possible to make a station that is not sequential and add it to the mosquito program and have it run the entire duration of the program. In this way, it acts as a program specific master station. I hope that makes sense and if it doesn’t, you are welcome to play with the demo available here: http://demo.opensprinkler.com (password: opendoor).
In regard to your second question, yes we support second granularity up to one minute.