Once the cucumber plants begins flowering then you should start seeing cucumbers growing on the cucumber plant within 10 to 15 or at least in 20 days after the cucumber flowering happens.
Cucumbers are usually ready to harvest from the plant within 2 to 3 months after planting the cucumber plant or as long as 5 to 6 months when you plant them from the seeds.
It can depend on your climate and how well you take care of them but within 2 to 3 months the cucumbers should be ready to harvest.