I'm just speculating (I have Burnout on disc and bought DLC separately), but I think once you download it all you should see the DLC packages as separate items to install on your XMB.
Double-check on PSN first to be sure, but the time-savers pack should have the red shopping bag on it, indicating you own it.
Then, delete the one on your PS3, install the others and then re-download the time-saver pack when you're ready for it, if ever.
Again, speculation on my part; I didn't buy all at once like you did.