Question about when to apply

I am applying for a fiancee visa next month.  I'm currently in the UK on a visitor's visa with a ticket home to the US for the 24th of Feb.  My fiance is joining me for 3.5 weeks.  Obviously the hope is that I will be able to return to the UK with him.  I will be purchasing the priority service but I have a conviction (which is spent but I will still declare to be on the safe side) and my fiance is in the midst of a divorce (has decree nisi and will supply a letter from his solicitor stating divorce is imminent).  I assume that these two things could potentially delay the processing.  So my questions are...

1.  Operating under the assumption it will take a few days to get a biometrics appointment, can I apply online a few days before leaving for the US in the hopes that I get a biometrics appt the next day after arriving home?  (This scares me a bit because what if something happens and I don't get home as planned?  I arrived here 26th of August so I assume my visa expires on the 26th of February so I have to be out of here no matter what) 

2.  Or is it better/safer to apply as soon as I'm on American soil and try to do a walk-in for the biometric appointment if the system gives me one days out?  (I can't imagine the application center in Cincinnati is overwhelmed but who knows).

Any advice/experience would be appreciated!

Thanks,
Lisa

You must be physically present in the US when you apply. The application asks specifically where you are at the moment you are filling out the form, you cannot be in the UK while doing it. You can do it the moment you land in the US if you want but you cannot do it before.

Unless you want to go down the road of potentially being accused of using deception on a visa application and filling it out when you are in the UK & saying you're in the US. Which is a REALLY BAD idea.

Wait until you return to the US.

Brilliant and thank you.  No plan on being deceptive.  I tried to do a bit of research and saw a post that was from 2009 essentially stating you could do such (apply from the UK) but I was afraid it was out of date or just plain wrong. 

I think I'll just show up to the application center the day after I arrive in the hopes that if my biometric appt is scheduled for days out they can squeeze me in. 

Thanks again,
Lisa

Brilliant and thank you.  No plan on being deceptive.  I tried to do a bit of research and saw a post that was from 2009 essentially stating you could do such (apply from the UK) but I was afraid it was out of date or just plain wrong. 

I think I'll just show up to the application center the day after I arrive in the hopes that if my biometric appt is scheduled for days out they can squeeze me in. 

Thanks again,
Lisa

Sounds like a plan...just an FYI-- any visa post that is more than 6 months old, is probably DANGEROUSLY out of date and the one that you mentioned is a specific example as to why it's good to disregard anything visa related that is older than that. Immigration Rules change too fast to rely on old information.