In a Presentation, you can adjust the times set by going into the HTML itself. I normally find it easier to first set the time using the Design Window user interface. After that has been set, switch to HTML view and locate the Playlist Item (or Placeholder) and adjust the time down to the minute.
In Schedules, this solution isn't available. You could try using a single Presentation in a Schedule, and then embed multiple Presentations in that main Presentation to achieve a similar effect.
+1 for the wishlist - I use RV for displays in my high school, and would really like to have more granular control over specific presentations at specific times (e.g. 5 min before class have a statis text show GET TO CLASS!)