Just got off the phone with DHL Japan.
Don't want to get anybody's hopes up but the representative told me that she thinks the hold on all Nintendo switches will be uplifted tonight. But, a big but, she cannot promise. If the hold is uplifted and catches the late flight tonight, the package will arrive in Singapore by tomorrow.
She made it clear that there are a ton of people experiencing the same problem and that Amazon is (now) aware of the battery regulations that is triggering the hold.
Fingers crossed.
Based on my tracking from Nagoya, the hold needs to be lifted before 530pm otherwise it'll miss the flight to HK and possibly delayed 1 day.