Does it really matter when I do the oil flush – before, during, or after using FTC Decarbonizer?

No, it doesn’t matter when you use the Flushing Oil Concentrate. If you’re close to the time of a scheduled oil change, you can wait until that time comes around. But if that is still a long way off, it is recommended to do the flush as soon as is convenient, just to get the full effect of what you are striving to achieve, as soon as possible.  FTC Decarbonizer and Flushing Oil Concentrate do different jobs, but they work extremely well together in overcoming a host of problems; blow-by and excessive oil burning being major ones. If you have both products available, it is recommended to start using the FTC Decarbonizer in the fuel as soon as possible and carry out the engine oil flush as soon as is convenient.
The lower ‘oil control’ ring on the piston gets pretty sludged and blocked over time, and that contributes to blowby/oil burning/carbon by-products etc. Flushing Oil Concentrate will de-sludge the oil control ring groove as well as the ‘drain-back’ slots in the piston ring groove. This action restores correct oil control on the cylinder walls.
Some engines that are badly sludged up sometimes need a second, follow-up flush in about 600 – 1000 miles (10 – 12 hours) from the first initial, concentrated flush. Instructions about this are on the Flushing Oil Concentrate Instruction Sheet. A good way to tell if a second, follow-up flush is needed is to check the color of the engine oil at about 500-ish miles since the initial flush. If the oil is once again very dark or even black at that time, the follow-up flush is recommended. If the oil isn’t super dirty and gritty looking, you can safely assume that the system is good and clean from the initial flush and you can just plan to use the Flushing Oil Concentrate with the next scheduled routine oil change. Information about that is also on the Instruction Sheet that is included with the product.