Sorry, I guess I was assuming you understood more than you do; I've forgotten already how overwhelming all of the information can feel. At the top of this forum are several threads that are marked with yellow "stickies"; these contain a wealth of information about understanding feline diabetes and how to manage the care of your diabetic cat. A protocol is simply a set of guidelines that you choose to follow that helps you know how much insulin to give, how to keep track of kitty's blood glucose, and how to decide when to make an adjustment to the dose.
There are two main protocols that most folks use - SLGS stands for Start Low, Go Slow. Since you're not able to test during the day, this is probably the one you'll want to follow. Complete guidelines are given here:
http://www.felinediabetes.com/FDMB/...-low-go-slow-slgs-tight-regulation-tr.210110/
This will help you make decisions about how to handle giving insulin, so please read it, then re-read it, and keep doing so until you understand it completely!
One thing to understand is that Lantus is a "depot" insulin - in the pen, it is contained in a slightly acidic liquid. Once it is injected under your cat's skin, into a neutral environment, the insulin precipitates out and forms a deposit of insulin that is taken up into the bloodstream slowly over a period of 12-14 hours. So even if you give a shot in the morning, it will continue working throughout the next 12 hours. When you reduce doses, it will take a few cycles before you can tell what effect the change has, because there is still insulin in the depot being used up.
Again, at a very minimum, read the stickies about the Insulin Depot and about the dosing methods (SLGS and TR). You can do this, from what I see on your spreadsheet, Carter doesn't appear to have been in any danger. Best thing you can do is get him on a consistent dose, monitor when you can (always test before shots!), keep your spreadsheet up-to-date, and get a curve when you're home on the weekends.
Please come back with any further questions you have - it takes a while to internalize all of this - and good luck!