The behaviour you are describing from the system is somewhat unexpected. If you make a change to a course and extract it, the change should be there immediately. The reason for this is that all course resources and settings go straight into the database without delay, and it is from the database that all course extractions are made.
That said, if you extract a course, make a change, then extract it again all within the space of about 5 minutes, a midstream ISP may have cached the first version of your course, and when you requested the same file 5 minutes later, the ISP assumes nothing has changed, and just gives you the old file. This is something ISPs do to save on their bandwidth costs. Your changes have indeed been made and have taken effect immediately, however, and it shouldn't be something you'll notice unless you are trying to extract the course repeatedly over a short time period.
Also, you may experience lag when you make alterations to themes or to assessments and preview them. The reason for this lag is the old css and xml that essentially comprise the 'meat' of the assessments and themes can be cached by your browser or a midstream ISP, and it can take up to a few minutes for your browser to realize the version it has and the version we have are not the same. But again, the changes are in fact immediately taking place on our end.
I hope that helps explain what is going on,
'Kris