I would suggest that you order just before you begin the conversion.
You have said that you will try to use up Bacq stuff before you convert, so how long will that take you? And, more importantly, since you know that conversion may cost $100 (50 gallons bleach at $2/gallon) plus a test kit ($70) can you use up that leftover stuff and not spend $170 on extra requirements?
Personally, I'd do a financial calculation of anticipated costs of continuing with Bacq vs selling the leftovers on Craigslist and converting now. You know that you can easily use 50 gallons of bleach, at <$2gallon (Sams club $8.40/4.26 gallons), maybe more, I dunno. Maybe less with a partial water change. And, you may be done in a matter of days -- late August, lots of time to swim in sparkly clean water in Aug, and Sept. You need to search the posts to see how long it might take. I think I recall some at just a few days, like 5 or 6, and some that took way, way longer to get the last parts (CC's ) into range. It may also be that a partial drain and fill will speed that along. Your choice.
But, really, you probably want to order maybe a month or so before you do the conversion. Time to get familiar with the tests. I'd order extra 0871 (?) for FC tests and stuff for CYA -- maybe. I got my test kit in April I think (search for my first posts to know for sure) and I am not yet out of FC tests, but did run out of CYA tests. I had to test CYA a lot since I had a leak and it kept changing and it took awhile to stabelize, plus I did it a few times in a row when I should have just poured the mix back into the bottle to try again. The CYA test is tricky.