Thats how long it will wait to turn on.
Typically used when you want 2 pumps running opposite of each other.
1 pump would have that set to 0 - then On Time of 30 seconds lets say
2nd pump initial off time would be 30 seconds
The 2nd pump wouldn't turn on until the first pump was turning off.
Set it to zero if you are using 1 pump or don't want them running opposite of each other