New pool owner with 18x4 Intex to startup

[I'mOnMyOwn]

HELP! I just purchased an Intex above ground pool 18x48. We have finally filled it and I started the PH decreaser as my PH level was the highest my tester would read at an 8.2. Now I am wondering how long after do I retest and add my multi functional chlorinated granules, and shock? Also how long one should wait and retest before it is safe to swim. The Academy employee gave us a ballpark figure of 36 hours....any sooner and we could possibly sustain chemical burns(way to terrify mom!). So since I as in mom wanted this pool and hubby was against it I have to maintain this big ol beast on my own. Any help would be extremely appreciated, also I have read quite a few threads about the BBB use, since we have already started prior to reading this we have already opened the crystal care system we have to use them now. Thank you all again for even reading this. Be Blessed!!