For the journey from Southampton to Heathrow, National Rail journeys to Wolwik, and thence to Heathrow by bus. How far is the bus station from the airport? How long would it take to walk from the bus stop to actually enter the terminal building?
I'm sorry Arif I don't know Wolwik. Can you check the spelling ?
( and I say this as someone who can't spell Alberkirkee, Massechewsits or Coneticut amongst many others )
Do you mean Warwick or perhaps Woolwich ?
To walk from Heathrow bus terminal to Terminal 1, T2 or T3 takes about 10 - 15 minutes. T4 and T5 require a further free airport bus journey - about 15 - 20 minutes.
The National Rail Journey Planner shows Southampton to WOKING by train and a coach from there or Southampton to Reading by train and a coach from there.
However, it's both faster and cheaper to take a National Express coach directly from Southampton to Heathrow. See www.nationalexpress.com.