Here is an example of how you can set the value of a fan to ON just 20 minutes before the schedule starts. You can download an example below made with variables and actual scheduleRefs.
The variables that need to be created aside from your points to create this are:
now (dateTime) - you need to create a dateTime variable that will be used to get the current time.
newTime (dateTime) - this variable is needed so that we can subtract the start of the schedule time with however minutes we want the difference to be
The rest are found by creating a scheduleRef to the equip you wish to use this on and adding it either through "Tags" option when creating program or through Add Variable in right menu with program open.
Download the below program file.