You will need to plan this carefully, best a few months before your points actually expires. The reason for this is basically this, you can only redeem points to miles in block of 1,000 points for 2,000 miles (http://www.dbs.com/sg/personal/rewards/frameset.aspx)

So any balance miles of 999 or less would be wasted. So planning is important, and don't over earn otherwise they go to waste. Having said that, you can always try your luck and ask DBS to "put back" those miles arguing that you had earn them recntly and they should not expire so soon.

Lastly, I woud NOT wait to transfer the miles on the last day of points expiry. Give yourself some buffer time, do a week before.

Good luck!