I think you need at least all 7 pounds of that stabilizer to get near CYA 30. Add it all because even if you overshoot, it's not the end of the world. Not sure how your weather is during the summer, but if it's gets really hot, you'll want the CYA higher than 30. I run mine at 50 year round in San Jose, CA so the sun doesn't burn off my FC too quickly. I usually dose my pool in the 6-8 FC range daily and never let it get below 4. I found that running the CYA less than 50, my daily FC usage would get me dangerously close or even under my minimum of 4 by the end of the day, so I bumped up my cya to slow down the burn off and now I've got a little leeway in case I can't add FC that day.
Make sure to give those socks a squeeze periodically, because that will help dissolve the stabilizer faster into the pool. It will go quickly. Don't be alarmed when you get a white cloud of stabilizer from the squeezing. It will disappear shortly once it mixes in the water. I would go ahead and start the SLAM right now and just assume that your CYA is in the pool, even though it won't show up on the test right away until it's all dissolved and mixed with the water. Just target FC 12 with pool math and dose away with liquid chlorine. Retest FC and dose back up to 12 as aften as possible (minimum 3 times a day) and the SLAM should go very quickly for you.
After the stabilizer is fully dissolved and mixed for about a day, test it so you know if you need to add more. If you do though, just realize that you will increase your FC (both shock level and regular maintenance level). Just follow the CYA/FC chart and you can't go wrong.
