Have done two stopovers in Singapore in the last year (19 and 11 hours). No problem but I would recommend booking a transit hotel otherwise you will be confined to a small transit area for the duration.
Update - I was able to check-in online, print my boarding passes and go straight to security/immigration at BKK with no checked bags (bypassing the airport check-in process). Gave me about 40 bonus minutes in the airport bar by my reckoning..
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