Ashford Middlesex is very close to Heathrow, so no time at all. Ashford Kent to Heathrow would take about three hours.
Kent, England - 1,442 square miles.
72.8 miles via M20
162 miles
39 miles
161 miles
4766 miles
235 miles
235 miles
103 miles
Which Mansfield and which Kent are you asking about?
Assuming you're in the UK, Kent is 1442 square miles.