Probably a dumb question but I have been advised to keep the chlorine at shock level until it holds overnight. Does that mean to the exact number?

Last night when I went to bed I brought the chlorine to 12ppm (cya of 20 or less...added stabilizer a few days ago) This morning at 9:00 my chlorine was 10.5. It also rained last night. All numbers as of this morning....

FC 10.5
CC 0
PH 7.2
TA 80
CH 140 (working on raising to 200...concrete/guinite pool)
CYA waiting to test

The water is clear...not "sparkling" clear...especially in the deep end but it is clear and a pretty bluish color. Do I need to keep the level at 12ppm throughout the day today and again tonight or can I let it drop to the appropriate number per Best Guess chart?

Thanks!
Andrea