The ends of the Flow™ Frames are visible by taking the cover off one end of the hive box. It is worth having a look at the bees regularly through this window as you’ll get to know your hive and it doesn’t disturb the bees. You will see the bees depositing honey in the cells and, when the cells are full, sealing them with a wax capping.
When the end cells are full and capped this generally indicates that the honey is ready / ripe. There is no hurry though, the sealed honey will keep until it is convenient for you to drain it out of the hive.