Harvest:
Harvest cucumbers as soon as they reach mature size; cucumbers left on the vine past maturity will suppress the production of new flowers and fruit.

Slicing cucumbers are best picked when they are 6 to 8 inches long.

Pickling cucumbers–sweet or dill–are best picked when 1 to 6 inches long. Pick pickling cucumbers every two days.

Regular dills are best picked when 3 to 4 inches long.

Burpless cucumbers should be picked at about 10 inches long.

Hothouse-grown English or Armenian cucumbers are best picked when 12 to 15 inches long.

For more information on growing Cucumbers, check out this great guide from Harvest To Table:
https://harvesttotable.com/how_to_grow_cucumber/