Attending appointment after visa expiry date

Hi, so I am applying for ILR set (O) on Ancestry and my current 5 year visa expires on Dec 31, 2018. I am currently in Canada on holiday and will be returning to the UK on Dec 28. I don't believe it would be wise to apply online until I am back on UK soil as the first question of the online application is 'are you applying from the UK?', and it will not let you complete the application if the answer is no. The moment I return on the 28th I will submit my application. However I can only book my appointment until I have sent the application first so I can't tell how easy it will be to get an appointment before the expiry date. It seems to me that the recognized date of submission is considered the online application date and not the appointment.
So my question is, will my application be rejected if I attend the appointment after the expiry date?

I think application submission date is considered only. U will be fine with this as long as u apply before expiry of ur visa.
U cannot apply online from abroad as if u travel after applying, ur application is considered to be withdrawn.