You won't have to enter your schedule - there's APIs for Calendars. You'd just have to determine which calendars are considered "busy". As for upkeep, I found

You won't have to enter your schedule - there's APIs for Calendars. You'd just have to determine which calendars are considered "busy". As for upkeep, I found that the app is self-motivating. It's not measuring anything so if you miss an hour or a month it doesn't matter, there's no overwhelming guilt. The only thing you miss is being able to review what you worked on.