It’s a question I am always asked. Either for planning purposes.. or because they want to know how long they will be subjected to photographs for haha!
For me, the photograph time after the ceremony is used for;
Bride and groom portraits
I know some photographers like to take the bride and groom out at other points of the day. But my personal preference is to do all the important photographs in the time after the ceremony. This way, the rest of the day will be candid photographs etc
A venue usually gives an hour and a half for photographs. I agree with this and it is more than adequate. Even an hour can be fine with good organisation!
However, for small weddings and if the couple don’t particularly want a lot of family photographs – it can be much shorter.
Hope this helps in some way!