20 minutes is not long enough to wait for it to dry. Yes, it might look dry. It's not. You will have easier blushing results regardless of strength if you apply liberally, then allow it to dry a good 24 hours. If you don;t have that long, I'd at the least apply say frst thing in the morning and then wait until mid afternoon. Trying to blush it properly with too much residual moisture in the stock is very frustrating and it never seems to color the way you'd envision and typically requires overheating, which might cause other issues.
I know a number of people from years past who used to apply, let it dry a good while, then slop the stock with oil and heat it at that point. It's an interesting way to approach it - not my favored way, but it does work and typically goes quite dark. It obviously prohibits either multiple applications as well as neutralizing if so desired.
