You can't have them both… Either, you start a process yourself, passing in parameters OR you have your process start itself at some given point in time (possibly multiple times) by itself without passing parameters.
If you want to have the timer-started workflow behave differently, depending on certain values, add an additional service-task (or use a gateway) which uses services in YOUR environment, capable of accessing the values the process needs (e.g.. spring-beans, …).