Okay, the process for getting married is:
- in England and Wales, you must be resident in the county you wish to marry for 7 days before giving notice
- you then give notice to marry
- after giving notice, there is a mandatory 28-day wait before you can marry... this applies to everyone whether they are UK citizens or not.
- However, if you are subject to immigration control (you have any type of visa), your case may be referred to UKVI for further investigation (to check the marriage/relationship is genuine). If this happens, you may have to wait 70 days instead of the usual 28 days.
- However, if you have a fiance visa, you have already been approved by UKVI to marry in the UK (that's the purpose of your visa), so it's unlikely your case will be referred and that you will have to wait more than noramal 28 days after giving notice before you can marry.
I would give notice first, and then depending on how long you are told you will have to wait (i.e. if you're referred to UKVI or not), you can book the ceremony later.