FBlinkDownTime

This refers to how long it takes for the character's eyelids to go from up to down, and stay down. The default for this variable is 0.200 seconds. The time value is means that the eye will stay closed for about 0.1 seconds, and the speed of the eyelid from up to down will be 0.1 seconds (about half the time each). Increasing this value means that the character will take longer to close their eyelids, and the eyelids will stay down longer as well.

How long it takes to complete one blink does not seem to matter to the Min and Max blinking time variables - if it takes 15 seconds to blink once, the timer that determines when the next blink will take place will only start once blinking has commenced.