Judging by the fact that Steveoneil has yet to start his flying training and is asking such a basic question it seems to me the above answers are a bit complex.
Steve, assuming you're going to be flying a C150 or PA28 (typical UK training aircraft), work on a speed of 90 knots or 1.5 nautical miles per minute.
Therefore, divide the distance from the airport to your mums house (in nautical miles ideally but "normal" statute miles will be near enough if its not too far) by 1.5 to get the approximate flying time in minutes.
For example, if her house is 30 miles away, divide 30 by 1.5 = 20 minutes flying time.