That depends entirely upon what you have included in your ceremony and any extra activities you have planned.
The actual Ceremony may run from 20 minutes to an hour, however you might need to book for set-up & preparation time, any extra time needed for photographs, greetings etc. or even for an on-site the reception etc.
Time should also be allowed for dismantling and removal of the set-up.
The quickest set-up time I have had is about 5 minutes and the longest was about 40 minutes where decorations and equipment had to carried across a field.
Once your Ceremony script has been agreed upon, I can advise you on how long it will run, how much set-up & take-down time is required but you will be in control of other aspects such as the time your vendors (photographer, decorator etc.) require.
Thanks! And thanks for sharing your great posts every week!