Overview:
This function returns the minimum time that each flowitem must reside in the Rack. When the flowitem enters the Rack, it executes this function, and creates an event in the returned. After the time has expired, the Rack releases the item. If this function returns a value of -1, the Rack will not create an event to release the item at all, and you will need to release the item explicitly using the releaseitem() command. This can be used if you want to implement your own releasing strategy for the Rack.
Access variables:
current: the current object
item: the involved flowitem
port: the port the product entered through
