score:5
Having added an extra month to my time in the UK by mistake on the forms were of no consequence in my application. I had provided documents to support a 3 week stay however mistakenly put in an extra month in the time I would be in the UK.
My visa was approved. I suspect this is due to good travel history (4 UK Visitor visas and a valid US visa still) and good financials / ties to home country shown.