Fast Cycle?

Eight days ago I added about 80 Lbs. of Marshall Island rock (uncured)
to my new 75 Gal. Not being too familiar with liverock, I wasn't too
sure what to expect. When I opened the boxes, I got a slightly
unpleasant whiff and proceded to pick off any obvious dying stuff
along with as much macro as I could. Gave the rock a good swish around
in some aged sal****er I had made up in advance and plunked it into
the tank. Day 2 I tested for Ammonia and it was off the chart (no
surprise). Now, day 8 I test again...Zero. I then test for
nitrite....Zero. Next, Nitrate...Zero. Is it possible that my cycle
completed this quick? Everything I have read led me to believe 6 to 8
weeks especially using uncured.

Other paramaters:

temp-79
sg-1.024
PH- 8.0
skimmer- 24/7
circulation- ~500g/hr through sump supplemented with 4-Maxi-jet 900's.
Lighting- 440W VHO (2-50/50 2-Actinic) about 2 hrs./day right now
3-4" dead Aragonite sb
Using RO/DI for initial fill and top-off
Using SeaTest test kits

Is this typical? If so, do you think I should seed my SB now with some
LS?

Thanks!
-Scott