It would be enough if you take your time to browse the Humble Administrator's Garden and the Lingering Garden. Two classic gardens, one large and one small.
Go to the Humble Administrator's Garden first and then to the Liouyuan.
Really have time to go to Cold Mountain Temple.
South Square of Railway Station take Tour 2 (via 2 stops|16 minutes) and get off at Qimen, walk 606 meters to reach
Suzhou Museum (The Humble Administrator's Garden - Lion's Grove) take Tour 1 (via 8 stops|31 minutes) to the Liouyuan Garden