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Yes it would be an issue and a refusal because you were not physically present in the UK at that time 3 years ago (based on the quote above by yourself). You would either need to apply now or at least a few days or 1 week before 15th April or only after 13th May (based on when you returned to the UK 3 years ago).From 15-April-2012 and returned on 13-May-2012 = Total days absence = 29
Once you receive your approval, you will only 21 days to book your ceremony. The ceremony must be attended within 3 months of your approval letter.1- Is there any bank statement required with a specific amount showed in it ? No not required. Income and employment are not a requirement for naturalisation but you should complete the form truthfully.
2- What is the processing time these days ? Let's suppose if I apply on 1st April and everything is correct when can I expect the decision of my application ? Approvals can take anywhere between a 4 weeks and 6 months. Mine took about 5.5 weeks.