As others have said - it's all about the cotton and how much you have. What I generally check after I do a rebuild:
First - After I've broken in the build, I open up my RDA to look at the deck. I check the cotton and it should look a bit dry near the coils. I drip 3 or 4 drops directly on the cotton. I make sure the deck isn't flooded/drencheced.
Second - I vape till I get a dry/scratchy hit. I sorta count how many draws I get (sometimes 5 sometimes 10). The type of juice you use also contributes to how many drops, wetness, etc... I can also tell by taste and flavor dropp off.
Third - I open the deck back up, I look at the cotton. I make sure it's really dry near the coils. I may need to remove cotton if it's not wicking right, again it's all about the juice, your taste etc..
Fourth - Enjoy and keep on adjusting.
For me, I notice that my deck starts to flood or the taste is way off when I need to re-wick. It's always a learning process. Good luck!