When does the fermenting clock start?

My instructions say to leave it in primary for 6 days then transfer to secondary. It's been about 24 hours and the fermenting hasn't really started, though after reading all the posts I understand this is normal.

So, does the 6 day countdown to secondary begin when the brew starts to noticeably ferment or is it just six days from when it first entered the bucket, regardless of when it starts bubblin'?

There's no "one right time" to make the transfer. You definitely want to wait a few days after the active fermentation has subsided, but you could wait just a few days or a week or two. So, don't sweat the countdown too much.

I know you're probably anxious to taste the fruits of your labor, but, unfortunately, brewing is a hobby where patience is rewarded far more than haste. That's why people often have 3 or 4 batches in various stages of brewing at a time!

First, you probably shouldn't go by the kit instructions. They almost always rush your beer. Second, don't worry about moving to a secondary unless you'll be doing some long-term bulk aging, dry hopping, etc.

With that out of the way, the fermentation clock isn't all that important. Ideally, you'd want to pitch your yeast and have an active fermentation going shortly after, but it does take a day or two for some brews to really get going. That is fine. Either way, you should plan on leaving the beer in the primary bucket for at least a week or two. But the instructions say just 6 days? So what. Sure, you can still make beer after just 6 days in the fermenter, but give it a little more time and you will be rewarded.

Once you're getting ready to bottle just be sure to take a hydrometer sample a few days in a row and make sure you're close to your target gravity and see that the gravity hasn't changed after a few consecutive samples. This means your beer is done fermenting and safe to bottle.

You will have good beer.