The SAP system operates "in real time," however, the usefulness is somewhat reduced due to the server not being able to process all the requests we throw at it in "real time."
Requests made immediately (within the first minute of the SAP period) will take up to about 45 minites to process and the times get worse the further in to the SAP period you get.
What you end up with is an exercise in frustration as you spend 24 hours trying to make one little change to your schedule. Also, you need to be sure that you're off or on a break right when the SAP opens, otherwise you miss most of the good stuff.
If/when the system works in a timely fashion, SAP is great. It went much smoother in November and December when less people were moving things around to avoid losing their holiday pay due to our poorly written holiday pay agreement.