You must be a slow walker!
I'd say it takes less than 30 mins (about 25mins at my usual pace) to walk from the station to Thomond Park.
If you haven't chartered your own shuttle bus, then you could walk down to the bus stops outside Dunnes Stores on Henry St (10mins) and get a bus from there.
If I was walking, I'd go down Mallow St, over Shannon Bridge and up Shelbourne Road.
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