Does anyone know if you have to dust up the Shamrocks right up to Fully Grown before you can see if it's a 4-leaf, or can you tell before? Thanks :)

No- the 3 or 4 leaves will only show when it's fully grown.

Shame; thanks for the swift reply Roxanne :)

With all of mine, I used 8 DD per plant to get about 11 minutes away from the FG status, waited those 11 minutes and then started the process again till I landed with what I have now. But honestly, it's a diamond draining process. :D

I'm having a heck of a time getting a 4 leaf clover...  just one... one is all I ask lol  I've gone through so many diamonds today in search of one. 

Tip: let the plant go a few minutes past fully grown before ripping it up. Thought my Xth plant was again a 3-leaf - pretty sure it'd reached fully grown - was about to rip it up again. I came on here to see the reply, went back to start again and it was a 4-leaf. Shocked but happy. Good luck

I finally managed to get two in a row after going through about 25 prior to that lol

Actually, at the very second it reaches the FG status, there is no change.
When I did mine I left them at (Growing Happily) 28%, they all had a little over 11 minutes before being Fully grown, and then at exactly the second they changed from Growing Happily to Fully Grown it still was 28%. 
There is no delay, there is,however a small distinction in the size of the leaves. While it's growing the 3 leaves are a little bit smaller than what they are when they are fully grown. :)

what happens when it's a 4 clover?

Gives 25 gold when harvested.