Google maps is great to use, look it up. It says it takes 12 mins.
The A1 service to the airport leaves from outside the station - think it's stop B
No need to walk all the way to the bus station. Just walk out front of the main entrance of the train station and you'll see a couple of bus stops. The airport bus (A1) stops here at the train station.
Below is a link to the bus timetable for the A1 service. To see different days as it will pobably launch for you on the current days times, just click the red view PDF button to see the times of this service on other days.
Sun magic, that’s great information, do you have to book in advance for the bus to the airport
You can pay as you board, contactless or cash is accepted. Not sure what the fares are - although i do know the fares are branded on the outside of the bus as I've seen it pass me! :-)
The bus is operated by Transdev, it might have fares on their website - and there's an option to download the app where you can also buy tickets in the app too - you would just need to scan a QR code in the app to the drivers ticket machine.
Edit to add....
They do have fares on that link - you would probably want a single journey £5 per adult, or an airport return £10. Possibly an airport group return might be an option depending on how many there are in your group.
Correction to the above - an airport return ticket is £6 for an adult, and not £10 which is what I'd mentioned.