I have to agree with Tagnum, my wife and I tried to get a visitor visa before we got married (she has family, previous travel, a job, money etc) to fulfill all the requirements and we were denied. This is not saying you will be denied if you do apply, but the likelihood is high.
The best way would be to get married and get all your paperwork done early. Make sure you have lots of proof that it is a genuine relationship (receipts, photos, air travel etc etc).
The timeline says 14 months but some are faster and so may not take as long. Some people seem to be done in 6 or 7 months.
Hope this helps