What is a good approach to enable workers on the ground to "willing difficult project into existence in a bigger corp? Typically, ground workers (devs) plate i

What is a good approach to enable workers on the ground to "willing difficult project into existence in a bigger corp? Typically, ground workers (devs) plate is overflowing with work, coming from product management which are just increments or maintenance of existing products. There is not much Slack build into the daily processes to allow for rough ideation, concretization and much less implementation/prototyping. Other then allow for a certain amount of dev time to go into innovation (a la googles Friday off for personal project) i can't think of much. What is a good percentage of dev time to go into innovation 10%, 25%, ...? Second question: how do you derisk?